Separation matrix

ABSTRACT

The invention relates to a separation matrix comprising at least 11 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein:a) the ligands comprise multimers of alkali-stabilized Protein A domains, andb) the porous support comprises cross-linked polymer particles having a volume-weighted median diameter (d50, v) of 56-70 micrometers and a dry solids weight of 55-80 mg/ml.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Application No. 16,893,574, filed Jun. 5, 2020, which is a continuation of U.S. application Ser. No. 16/682,855, filed Nov. 13, 2019, now U.S. Pat. No. 10,711,035, which is a continuation of U.S. application Ser. No. 16/096,952, filed Oct. 26, 2018, now U.S. Pat. No. 10,513,537 issued Dec. 24, 2019, which claims the priority benefit of PCT/EP2017/061164 filed on May 10, 2017 which claims priority benefit of U.S. application Ser. No. 15/282,367, filed Sep. 30, 2016 and Great Britain Application Nos. 1608229.9 and 1608232.3, both of which were filed May 11, 2016. The entire contents of which are hereby incorporated by reference herein.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Oct. 22, 2018, is named 313838A_ST25.txt and is 79,053 bytes in size.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of affinity chromatography, and more specifically to mutated immunoglobulin-binding domains of Protein A, which are useful in affinity chromatography of immunoglobulins. The invention also relates to multimers of the mutated domains and to separation matrices containing the mutated domains or multimers.

BACKGROUND OF THE INVENTION

Immunoglobulins represent the most prevalent biopharmaceutical products in either manufacture or development worldwide. The high commercial demand for and hence value of this particular therapeutic market has led to the emphasis being placed on pharmaceutical companies to maximize the productivity of their respective mAb manufacturing processes whilst controlling the associated costs.

Affinity chromatography is used in most cases, as one of the key steps in the purification of these immunoglobulin molecules, such as monoclonal or polyclonal antibodies. A particularly interesting class of affinity reagents is proteins capable of specific binding to invariable parts of an immunoglobulin molecule, such interaction being independent on the antigen-binding specificity of the antibody. Such reagents can be widely used for affinity chromatography recovery of immunoglobulins from different samples such as but not limited to serum or plasma preparations or cell culture derived feed stocks. An example of such a protein is staphylococcal protein A, containing domains capable of binding to the Fc and Fab portions of IgG immunoglobulins from different species. These domains are commonly denoted as the E-, D-, A-, B- and C-domains.

Staphylococcal protein A (SpA) based reagents have due to their high affinity and selectivity found a widespread use in the field of biotechnology, e.g. in affinity chromatography for capture and purification of antibodies as well as for detection or quantification. At present, SpA-based affinity medium probably is the most widely used affinity medium for isolation of monoclonal antibodies and their fragments from different samples including industrial cell culture supernatants. Accordingly, various matrices comprising protein A-ligands are commercially available, for example, in the form of native protein A (e.g. Protein A SEPHAROSE, GE Healthcare, Uppsala, Sweden) and also comprised of recombinant protein A (e.g. rProtein A-SEPHAROSE, GE Healthcare). More specifically, the genetic manipulation performed in the commercial recombinant protein A product is aimed at facilitating the attachment thereof to a support and at increasing the productivity of the ligand.

These applications, like other affinity chromatography applications, require comprehensive attention to definite removal of contaminants. Such contaminants can for example be non-eluted molecules adsorbed to the stationary phase or matrix in a chromatographic procedure, such as non-desired biomolecules or microorganisms, including for example proteins, carbohydrates, lipids, bacteria and viruses. The removal of such contaminants from the matrix is usually performed after a first elution of the desired product, in order to regenerate the matrix before subsequent use. Such removal usually involves a procedure known as cleaning-in-place (CIP), wherein agents capable of eluting contaminants from the stationary phase are used. One such class of agents often used is alkaline solutions that are passed over said stationary phase. At present the most extensively used cleaning and sanitizing agent is NaOH, and the concentration thereof can range from 0.1 up to e.g. 1 M, depending on the degree and nature of contamination. This strategy is associated with exposing the matrix to solutions with pH-values above 13. For many affinity chromatography matrices containing proteinaceous affinity ligands such alkaline environment is a very harsh condition and consequently results in decreased capacities owing to instability of the ligand to the high pH involved.

An extensive research has therefore been focused on the development of engineered protein ligands that exhibit an improved capacity to withstand alkaline pH-values. For example, Gülich et al. (Susanne Gülich, Martin Linhult, Per-Åke Nygren, Mathias Uhlén, Sophia Hober, Journal of Biotechnology 80 (2000), 169-178) suggested protein engineering to improve the stability properties of a Streptococcal albumin-binding domain (ABD) in alkaline environments. Gülich et al. created a mutant of ABD, wherein all the four asparagine residues have been replaced by leucine (one residue), aspartate (two residues) and lysine (one residue). Further, Gülich et al. report that their mutant exhibits a target protein binding behavior similar to that of the native protein, and that affinity columns containing the engineered ligand show higher binding capacities after repeated exposure to alkaline conditions than columns prepared using the parental non-engineered ligand. Thus, it is concluded therein that all four asparagine residues can be replaced without any significant effect on structure and function.

Recent work shows that changes can also be made to protein A (SpA) to effect similar properties. US patent application publication US 2005/0143566, which is hereby incorporated by reference in its entirety, discloses that when at least one asparagine residue is mutated to an amino acid other than glutamine or aspartic acid, the mutation confers an increased chemical stability at pH-values of up to about 13-14 compared to the parental SpA, such as the B-domain of SpA, or Protein Z, a synthetic construct derived from the B-domain of SpA (U.S. Pat. No. 5,143,844, incorporated by reference in its entirety). The authors show that when these mutated proteins are used as affinity ligands, the separation media as expected can better withstand cleaning procedures using alkaline agents. Further mutations of protein A domains with the purpose of increasing the alkali stability have also been published in U.S. Pat. No. 8,329,860, JP 2006304633A, U.S. Pat. No. 8,674,073, US 2010/0221844, US 2012/0208234, U.S. Pat. No. 9,051,375, US 2014/0031522, US 2013/0274451 and WO 2014/146350, all of which are hereby incorporated by reference in their entireties. However, the currently available mutants are still sensitive to alkaline pH and the NaOH concentration during cleaning is usually limited to 0.1 M, which means that complete cleaning is difficult to achieve. Higher NaOH concentrations, which would improve the cleaning, lead to unacceptable capacity losses.

There is thus still a need in this field to obtain a separation matrix containing protein ligands having a further improved stability towards alkaline cleaning procedures. There is also a need for such separation matrices with an improved binding capacity to allow for economically efficient purification of therapeutic antibodies.

SUMMARY OF THE INVENTION

One aspect of the invention is to provide a polypeptide with improved alkaline stability. This is achieved with an Fc-binding polypeptide comprising a mutant of a parental Fc-binding domain of Staphylococcus Protein A (SpA), as defined by, or having at least 80% such as at least 90%, 95% or 98% identity to, SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO:3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:22, SEQ ID NO:51 or SEQ ID NO:52, wherein at least the asparagine or serine residue at the position corresponding to position 11 in SEQ ID NO:4-7 has been mutated to an amino acid selected from the group consisting of glutamic acid, lysine, tyrosine, threonine, phenylalanine, leucine, isoleucine, tryptophan, methionine, valine, alanine, histidine and arginine. Alternatively, the polypeptide comprises a sequence as defined by, or having at least 80% or at least 90%, 95% or 98% identity to SEQ ID NO:53.

 (SEQ ID NO: 53) X₁Q X₂AFYEILX₃LP NLTEEQRX₄X₅F IX₆X₇LKDX₈PSX₉ SX₁₀X₁₁X₁₂LAEAKX₁₃ X₁₄NX₁₅AQ wherein individually of each other: X₁=A or Q or is deleted X₂=E, K, Y, T, F, L, W, I, M, V, A, H or R X₃=H or K X₄=A or N X₅=A, G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K X₆=Q or E X₇=S or K X₈=E or D X₉=Q or V or is deleted X₁₀=K, R or A or is deleted X₁₁=A, E or N or is deleted X₁₂=I or L X₁₃=K or R X₁₄=L or Y X₁₅=D, F, Y, W, K or R

One advantage is that the alkaline stability is improved over the parental polypeptides, with a maintained highly selective binding towards immunoglobulins and other Fc-containing proteins.

A second aspect of the invention is to provide a multimer with improved alkaline stability, comprising a plurality of polypeptides. This is achieved with a multimer of the polypeptide disclosed above.

A third aspect of the invention is to provide a nucleic acid or a vector encoding a polypeptide or multimer with improved alkaline stability. This is achieved with a nucleic acid or vector encoding a polypeptide or multimer as disclosed above.

A fourth aspect of the invention is to provide an expression system capable of expressing a polypeptide or multimer with improved alkaline stability. This is achieved with an expression system comprising a nucleic acid or vector as disclosed above.

A fifth aspect of the invention is to provide a separation matrix capable of selectively binding immunoglobulins and other Fc-containing proteins and exhibiting an improved alkaline stability. This is achieved with a separation matrix comprising at least 11 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein:

a) the ligands comprise multimers of alkali-stabilized Protein A domains,

b) the porous support comprises cross-linked polymer particles having a volume-weighted median diameter (d50, v) of 56-70 micrometers and a dry solids weight of 55-80 mg/ml. Alternatively, it is achieved with a separation matrix comprising at least 15 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein said ligands comprise multimers of alkali-stabilized Protein A domains.

One advantage is that a high dynamic binding capacity is provided. A further advantage is that a high degree of alkali stability is achieved.

A sixth aspect of the invention is to provide an efficient and economical method of isolating an immunoglobulin or other Fc-containing protein. This is achieved with a method comprising the steps of:

a) contacting a liquid sample comprising an immunoglobulin with a separation matrix as disclosed above,

b) washing the separation matrix with a washing liquid,

c) eluting the immunoglobulin from the separation matrix with an elution liquid, and

d) cleaning the separation matrix with a cleaning liquid.

Further suitable embodiments of the invention are described in the dependent claims. Co-pending applications PCT EP2015/076639, PCT EP2015/076642, GB 1608229.9 and GB 1608232.3 are hereby incorporated by reference in their entireties.

Definitions

The terms “antibody” and “immunoglobulin” are used interchangeably herein, and are understood to include also fragments of antibodies, fusion proteins comprising antibodies or antibody fragments and conjugates comprising antibodies or antibody fragments.

The terms an “Fc-binding polypeptide” and “Fc-binding protein” mean a polypeptide or protein respectively, capable of binding to the crystallisable part (Fc) of an antibody and includes e.g. Protein A and Protein G, or any fragment or fusion protein thereof that has maintained said binding property.

The term “linker” herein means an element linking two polypeptide units, monomers or domains to each other in a multimer.

The term “spacer” herein means an element connecting a polypeptide or a polypeptide multimer to a support.

The term “% identity” with respect to comparisons of amino acid sequences is determined by standard alignment algorithms such as, for example, Basic Local Alignment Tool (BLAST) described in Altshul et al. (1990) J. Mol. Biol., 215: 403-410. A web-based software for this is freely available from the US National Library of Medicine at blast.ncbi.nlm.nih.gov/Blast.cgi?PROGRAM=blastp&PAGE_TYPE=BlastSearch&LINK_LOC=blasthome. Here, the algorithm “blastp (protein-protein BLAST)” is used for alignment of a query sequence with a subject sequence and determining i.a. the % identity.

As used herein, the terms “comprises,” “comprising,” “containing,” “having” and the like can have the meaning ascribed to them in U.S. Patent law and can mean “includes,” “including,” and the like; “consisting essentially of” or “consists essentially” likewise has the meaning ascribed in U.S. Patent law and the term is open-ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows an alignment of the Fc-binding domains as defined by SEQ ID NO:1-7 and 51-52.

FIG. 2 shows results from Example 2 for the alkali stability of parental and mutated tetrameric Zvar (SEQ ID NO:7) polypeptide variants coupled to an SPR biosensor chip.

FIG. 3 shows results from Example 4 for the alkali stability (0.5 M NaOH) of parental and mutated tetrameric Zvar (SEQ ID NO:7) polypeptide variants coupled to agarose beads.

FIG. 4 shows results from Example 4 for the alkali stability (1.0 M NaOH) of parental and mutated tetrameric Zvar (SEQ ID NO:7) polypeptide variants coupled to agarose beads.

FIG. 5 shows results from Example 7 for the alkali stability (1.0 M NaOH) of agarose beads with different amounts of mutated multimer variants (SEQ ID NO:20) coupled. The results are plotted as the relative remaining dynamic capacity (Qb10%, 6 min residence time) vs. incubation time in 1 M NaOH.

FIG. 6 shows results from Example 7 for the alkali stability (1.0 M NaOH) of agarose beads with different amounts of mutated multimer variants (SEQ ID NO:20) coupled. The results are plotted as the relative remaining dynamic capacity (Qb10%, 6 min residence time) after 31 h incubation in 1 M NaOH vs. the ligand content of the prototypes.

DETAILED DESCRIPTION OF EMBODIMENTS

In one aspect the present invention discloses an Fc-binding polypeptide, which comprises, or consists essentially of, a mutant of an Fc-binding domain of Staphylococcus Protein A (SpA), as defined by, or having at least 90%, at least 95% or at least 98% identity to, SEQ ID NO:1 (E-domain), SEQ ID NO:2 (D-domain), SEQ ID NO:3 (A-domain), SEQ ID NO:22 (variant A-domain), SEQ ID NO:4 (B-domain), SEQ ID NO:5 (C-domain), SEQ ID NO:6 (Protein Z), SEQ ID NO:7 (Zvar), SEQ ID NO:51 (Zvar without the linker region amino acids 1-8 and 56-58) or SEQ ID NO:52 (C-domain without the linker region amino acids 1-8 and 56-58) as illustrated in FIG. 1 , wherein at least the asparagine (or serine, in the case of SEQ ID NO:2) residue at the position* corresponding to position 11 in SEQ ID NO:4-7 has been mutated to an amino acid selected from the group consisting of glutamic acid, lysine, tyrosine, threonine, phenylalanine, leucine, isoleucine, tryptophan, methionine, valine, alanine, histidine and arginine. Protein Z (SEQ ID NO:6) is a mutated B-domain as disclosed in U.S. Pat. No. 5,143,844, hereby incorporated by reference in its entirety, while SEQ ID NO:7 denotes a further mutated variant of Protein Z, here called Zvar, with the mutations N3A, N6D, N23T. SEQ ID NO:22 is a natural variant of the A-domain in Protein A from Staphylococcus aureus strain N315, having an A46S mutation, using the position terminology of FIG. 1 . The mutation of N11 in these domains confers an improved alkali stability in comparison with the parental domain/polypeptide, without impairing the immunoglobulin-binding properties. Hence, the polypeptide can also be described as an Fc- or immunoglobulin-binding polypeptide, or alternatively as an Fc- or immunoglobulin-binding polypeptide unit.

-   -   Throughout this description, the amino acid residue position         numbering convention of FIG. 1 is used, and the position numbers         are designated as corresponding to those in SEQ ID NO:4-7. This         applies also to multimers, where the position numbers designate         the positions in the polypeptide units or monomers according to         the convention of FIG. 1 .

(truncated Zvar) SEQ ID NO: 51 QQ NAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQ (truncated C domain) SEQ ID NO: 52 QQ NAFYEILHLP NLTEEQRNGF IQSLKDDPSV SKEILAEAKK LNDAQ

In alternative language, the invention discloses an Fc-binding polypeptide which comprises a sequence as defined by, or having at least 90%, at least 95% or at least 98% identity to SEQ ID NO:53.

 (SEQ ID NO: 53) X₁Q X₂AFYEILX₃LP NLTEEQRX₄X₅F IX₆X₇LKDX₈PSX₉ SX₁₀X₁₁X₁₂LAEAKX₁₃ X₁₄NX₁₅AQ wherein individually of each other: X₁=A, Q or is deleted X₂=E, K, Y, T, F, L, W, I, M, V, A, H or R X₃=H or K X₄=A or N X₅=A, G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K, such as S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K X₆=Q or E X₇=S or K X₈=E or D X₉=Q, V or is deleted X₁₀=K, R, A or is deleted X₁₁=A, E, N or is deleted X₁₂=I or L X₁₃=K or R X₁₄=L or Y X₁₅=D, F, Y, W, K or R

Specifically, the amino acid residues in SEQ ID NO:53 may individually of each other be:

X₁=A or is deleted

X₂=E

X₃=H

X₄=N

X₆=Q

X₇=S

X₈=D

X₉=V or is deleted

X₁₀=K or is deleted

X₁₁=A or is deleted

X₁₂=I

X₁₃=K

X₁₄=L.

In certain embodiments, the amino acid residues in SEQ ID NO:53 may be: X₁=A, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L. In some embodiments X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D and one or more of X₁, X₉, X₁₀ and X₁₁ is deleted. In further embodiments, X₁=A, X₂=E, X₃=H, X₄=N, X₅=S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D, or alternatively X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=F, Y, W, K or R.

The N11 (X₂) mutation (e.g. a N11E or N11K mutation) may be the only mutation or the polypeptide may also comprise further mutations, such as substitutions in at least one of the positions corresponding to positions 3, 6, 9, 10, 15, 18, 23, 28, 29, 32, 33, 36, 37, 40, 42, 43, 44, 47, 50, 51, 55 and 57 in SEQ ID NO:4-7. In one or more of these positions, the original amino acid residue may e.g. be substituted with an amino acid which is not asparagine, proline or cysteine. The original amino acid residue may e.g. be substituted with an alanine, a valine, a threonine, a serine, a lysine, a glutamic acid or an aspartic acid. Further, one or more amino acid residues may be deleted, e.g. from positions 1-6 and/or from positions 56-58.

In some embodiments, the amino acid residue at the position corresponding to position 9 in SEQ ID NO:4-7 (X₁) is an amino acid other than glutamine, asparagine, proline or cysteine, such as an alanine or it can be deleted. The combination of the mutations at positions 9 and 11 provides particularly good alkali stability, as shown by the examples. In specific embodiments, in SEQ ID NO: 7 the amino acid residue at position 9 is an alanine and the amino acid residue at position 11 is a lysine or glutamic acid, such as a lysine. Mutations at position 9 are also discussed in copending application PCT/SE2014/050872, which is hereby incorporated by reference in its entirety.

In some embodiments, the amino acid residue at the position corresponding to position 50 in SEQ ID NO:4-7 (X₁₃) is an arginine or a glutamic acid.

In certain embodiments, the amino acid residue at the position corresponding to position 3 in SEQ ID NO:4-7 is an alanine and/or the amino acid residue at the position corresponding to position 6 in SEQ ID NO:4-7 is an aspartic acid. One of the amino acid residues at positions 3 and 6 may be an asparagine and in an alternative embodiment both amino acid residues at positions 3 and 6 may be asparagines.

In some embodiments the amino acid residue at the position corresponding to position 43 in SEQ ID NO:4-7 (X₁₁) is an alanine or a glutamic acid, such as an alanine or it can be deleted. In specific embodiments, the amino acid residues at positions 9 and 11 in SEQ ID NO: 7 are alanine and lysine/glutamic acid respectively, while the amino acid residue at position 43 is alanine or glutamic acid.

In certain embodiments the amino acid residue at the position corresponding to position 28 in SEQ ID NO:4-7 (X₅) is an alanine or an asparagine, such as an alanine.

In some embodiments the amino acid residue at the position corresponding to position 40 in SEQ ID NO:4-7 (X₉) is selected from the group consisting of asparagine, alanine, glutamic acid and valine, or from the group consisting of glutamic acid and valine or it can be deleted. In specific embodiments, the amino acid residues at positions 9 and 11 in SEQ ID NO: 7 are alanine and glutamic acid respectively, while the amino acid residue at position 40 is valine. Optionally, the amino acid residue at position 43 may then be alanine or glutamic acid.

In certain embodiments, the amino acid residue at the position corresponding to position 42 in SEQ ID NO:4-7 (X₁₀) is an alanine, lysine or arginine or it can be deleted.

In some embodiments the amino acid residue at the position corresponding to position 18 in SEQ ID NO:4-7 (X₃) is a lysine or a histidine, such as a lysine.

In certain embodiments the amino acid residue at the position corresponding to position 33 in SEQ ID NO:4-7 (X₇) is a lysine or a serine, such as a lysine.

In some embodiments the amino acid residue at the position corresponding to position 37 in SEQ ID NO:4-7 (X₈) is a glutamic acid or an aspartic acid, such as a glutamic acid.

In certain embodiments the amino acid residue at the position corresponding to position 51 in SEQ ID NO:4-7 (X₁₄) is a tyrosine or a leucine, such as a tyrosine.

In some embodiments, the amino acid residue at the position corresponding to position 44 in SEQ ID NO:4-7 (X₁₂) is a leucine or an isoleucine. In specific embodiments, the amino acid residues at positions 9 and 11 in SEQ ID NO: 7 are alanine and lysine/glutamic acid respectively, while the amino acid residue at position 44 is isoleucine. Optionally, the amino acid residue at position 43 may then be alanine or glutamic acid.

In some embodiments, the amino acid residues at the positions corresponding to positions 1, 2, 3 and 4 or to positions 3, 4, 5 and 6 in SEQ ID NO: 4-7 have been deleted. In specific variants of these embodiments, the parental polypeptide is the C domain of Protein A (SEQ ID NO: 5). The effects of these deletions on the native C domain are described in U.S. Pat. Nos. 9,018,305 and 8,329,860, which are hereby incorporated by reference in their entireties.

In certain embodiments, the mutation in SEQ ID NO:4-7, such as in SEQ ID NO:7, is selected from the group consisting of: N11K; N11E; N11Y; N11T; N11F; N11L; N11W; N11; N11M; N11V; N11A; N11H; N11R; N11E, Q32A; N11E, Q32E, Q40E; N11E, Q32E, K50R; Q9A, N11E, N43A; Q9A, N11E, N28A, N43A; Q9A, N11E, Q40V, A42K, N43E, L44I; Q9A, N11E, Q40V, A42K, N43A, L44I; N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y; Q9A, N11E, N28A, Q40V, A42K, N43A, L44I; Q9A, N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y; N11K, H18K, D37E, A42R, N43A, L44I; Q9A, N11K, H18K, D37E, A42R, N43A, L44I; Q9A, N11K, H18K, D37E, A42R, N43A, L44I, K50R; Q9A, N11K, H18K, D37E, A42R; Q9A, N11E, D37E, Q40V, A42K, N43A, L44I and Q9A, N11E, D37E, Q40V, A42R, N43A, L44I. These mutations provide particularly high alkaline stabilities. The mutation in SEQ ID NO:4-7, such as in SEQ ID NO:7, can also be selected from the group consisting of N11K; N11Y; N11F; N11L; N11W; N11I; N11M; N11V; N11A; N11H; N11R; Q9A, N11E, N43A; Q9A, N11E, N28A, N43A; Q9A, N11E, Q40V, A42K, N43E, L44I; Q9A, N11E, Q40V, A42K, N43A, L44I; Q9A, N11E, N28A, Q40V, A42K, N43A, L44I; N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y; Q9A, N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y; N11K, H18K, D37E, A42R, N43A, L44I; Q9A, N11K, H18K, D37E, A42R, N43A, L44I and Q9A, N11K, H18K, D37E, A42R, N43A, L44I, K50R.

In some embodiments, the polypeptide comprises or consists essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, SEQ ID NO:14, SEQ ID NO:15, SEQ ID NO:16, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:26, SEQ ID NO:27, SEQ ID NO:28, SEQ ID NO:29, SEQ ID NO:36, SEQ ID NO:37, SEQ ID NO:38, SEQ ID NO:39, SEQ ID NO:40, SEQ ID NO:41, SEQ ID NO:42, SEQ ID NO:43, SEQ ID NO:44, SEQ ID NO:45, SEQ ID NO:46, SEQ ID NO:47, SEQ ID NO:48, SEQ ID NO:49 and SEQ ID NO:50. It may e.g. comprise or consist essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:16, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:26, SEQ ID NO:27, SEQ ID NO:28 and SEQ ID NO:29. It can also comprise or consist essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:16, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:27, SEQ ID NO:28, SEQ ID NO:38, SEQ ID NO:40; SEQ ID NO:41; SEQ ID NO:42; SEQ NO:43, SEQ ID NO:44, SEQ ID NO:45, SEQ ID NO:46, SEQ ID NO:47 and SEQ ID NO:48.

In certain embodiments, the polypeptide comprises or consists essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of SEQ ID NO:54-70. comprises or consists essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of SEQ ID NO:71-75, or it may comprise or consist essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of SEQ ID NO:76-79. It may further comprise or consist essentially of a sequence defined by or having at least 90%, 95% or 98% identity to an amino acid sequence selected from the group consisting of SEQ ID NO:89-95.

The polypeptide may e.g. be defined by a sequence selected from the groups above or from subsets of these groups, but it may also comprise additional amino acid residues at the N- and/or C-terminal end, e.g. a leader sequence at the N-terminal end and/or a tail sequence at the C-terminal end.

Zvar (Q9A, N11E, N43A) SEQ ID NO: 8 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK Zvar (Q9A, N11E, N28A, N43A) SEQ ID NO: 9 VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSQ SAALLAEAKK  LNDAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43E, L44I) SEQ ID NO: 10 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKEILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 11 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (N11E, Q32A) SEQ ID NO: 12 VDAKFDKEQQ EAFYEILHLP NLTEEQRNAF IASLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11E) SEQ ID NO: 13 VDAKFDKEQQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11E, Q32E, Q40E) SEQ ID NO: 14 VDAKFDKEQQ EAFYEILHLP NLTEEQRNAF IESLKDDPSE SANLLAEAKK LNDAQAPK Zvar (N11E, Q32E, K50R) SEQ ID NO: 15 VDAKFDKEQQ EAFYEILHLP NLTEEQRNAF IESLKDDPSQ SANLLAEAKR LNDAQAPK Zvar (N11K) SEQ ID NO: 16 VDAKFDKEQQ KAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11K, H18K, S33K, D37E, A42R, N43A, L441, K50R, L51Y) SEQ ID NO: 23 VDAKFDKEQQ KAFYEILKLP NLTEEQRNAF IQKLKDEPSQ SRAILAEAKR YNDAQAPK Zvar (Q9A, N11E, N28A, Q40V, A42K, N43A, L44I) SEQ ID NO: 24 VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y) SEQ ID NO: 25 VDAKFDKEAQ KAFYEILKLP NLTEEQRAAF IQKLKDEPSQ SRAILAEAKR YNDAQAPK Zvar (N11K, H18K, D37E, A42R, N43A, L44I) SEQ ID NO: 26 VDAKFDKEQQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRAILAEAKK LNDAQAPK Zvar (Q9A, N11K, H18K, D37E, A42R, N43A, L44I) SEQ ID NO: 27 VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRAILAEAKK LNDAQAPK Zvar (Q9A, N11K, H18K, D37E, A42R, N43A, L44I, K50R) SEQ ID NO: 28 VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRAILAEAKR LNDAQAPK Zvar (Q9A, N11K, H18K, D37E, A42R) SEQ ID NO: 29 VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRNLLAEAKK LNDAQAPK B (Q9A, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 36 ADNKFNKEAQ EAFYEILHLP NLNEEQRNGF IQSLKDDPSV SKAILAEAKK LNDAQAPK C (Q9A, N11E, E43A) SEQ ID NO: 37 ADNKFNKEAQ EAFYEILHLP NLTEEQRNGF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (N11Y) SANLLAEAKK SEQ ID NO: 38 VDAKFDKEQQ YAFYEILHLP NLTEEQRNAF IQSLKDDPSQ LNDAQAPK Zvar (N11T) SEQ ID NO: 39 VDAKFDKEQQ TAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11F) SEQ ID NO: 40 VDAKFDKEQQ FAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11L) SEQ ID NO: 41 VDAKFDKEQQ LAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11W) SEQ ID NO: 42 VDAKFDKEQQ WAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11I) SEQ ID NO: 43 VDAKFDKEQQ IAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11M) SEQ ID NO: 44 VDAKFDKEQQ MAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11V) SEQ ID NO: 45 VDAKFDKEQQ VAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11A) SEQ ID NO: 46 VDAKFDKEQQ AAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11H) SEQ ID NO: 47 VDAKFDKEQQ HAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (N11R) SEQ ID NO: 48 VDAKFDKEQQ RAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SANLLAEAKK LNDAQAPK Zvar (Q9A, N11E, D37E, Q40V, A42K, N43A, L44I) SEQ ID NO: 49 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, D37E, Q40V, A42R, N43A, L44I) SEQ ID NO: 50 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SRAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29G, Q40V, A42K, N43A, L44I) SEQ ID NO: 54 VDAKFDKEAQ EAFYEILHLP NLTEEQRNGF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29S, Q40V, A42K, N43A, L44I) SEQ ID NO: 55 VDAKFDKEAQ EAFYEILHLP NLTEEQRNSF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29Y, Q40V, A42K, N43A, L44I) SEQ ID NO: 56 VDAKFDKEAQ EAFYEILHLP NLTEEQRNYF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29Q, Q40V, A42K, N43A, L44I) SEQ ID NO: 57 VDAKFDKEAQ EAFYEILHLP NLTEEQRNQF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29T, Q40V, A42K, N43A, L44I) SEQ ID NO: 58 VDAKFDKEAQ EAFYEILHLP NLTEEQRNTF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29N, Q40V, A42K, N43A, L44I) SEQ ID NO: 59 VDAKFDKEAQ EAFYEILHLP NLTEEQRNNF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29F, Q40V, A42K, N43A, L44I) SEQ ID NO: 60 VDAKFDKEAQ EAFYEILHLP NLTEEQRNFF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29L, Q40V, A42K, N43A, L44I) SEQ ID NO: 61 VDAKFDKEAQ EAFYEILHLP NLTEEQRNLF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29W, Q40V, A42K, N43A, L44I) SEQ ID NO: 62 VDAKFDKEAQ EAFYEILHLP NLTEEQRNWF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29I, Q40V, A42K, N43A, L44I) SEQ ID NO: 63 VDAKFDKEAQ EAFYEILHLP NLTEEQRNIF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29M, Q40V, A42K, N43A, L44I) SEQ ID NO: 64 VDAKFDKEAQ EAFYEILHLP NLTEEQRNMF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29V, Q40V, A42K, N43A, L44I) SEQ ID NO: 65 VDAKFDKEAQ EAFYEILHLP NLTEEQRNVF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29D, Q40V, A42K, N43A, L44I) SEQ ID NO: 66 VDAKFDKEAQ EAFYEILHLP NLTEEQRNDF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29E, Q40V, A42K, N43A, L44I) SEQ ID NO: 67 VDAKFDKEAQ EAFYEILHLP NLTEEQRNEF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29H, Q40V, A42K, N43A, L44I) SEQ ID NO: 68 VDAKFDKEAQ EAFYEILHLP NLTEEQRNHF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29R, Q40V, A42K, N43A, L44I) SEQ ID NO: 69 VDAKFDKEAQ EAFYEILHLP NLTEEQRNRF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, A29K, Q40V, A42K, N43A, L44I) SEQ ID NO: 70 VDAKFDKEAQ EAFYEILHLP NLTEEQRNKF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I, D53F) SEQ ID NO: 71 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNFAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I, D53Y) SEQ ID NO: 72 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNYAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I, D53W) SEQ ID NO: 73 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNWAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I, D53K) SEQ ID NO: 74 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNKAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I, D53R) SEQ ID NO: 75 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNRAQAPK Zvar (Q9del, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 76 VDAKFDKE_Q EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40del, A42K, N43A, L44I) SEQ ID NO: 77 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPS_ SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40V, A42del, N43A, L44I) SEQ ID NO: 78 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV S_AILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43del, L44I) SEQ ID NO: 79 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SK_ILAEAKK LNDAQAPK Zvar (D2del, A3del, K4del, Q9A, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 89 V___FDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (V1del, D2del, Q9A, N11E, Q40V, A42K, N43A, L44I, K58del) SEQ ID NO: 90 __AKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAP_ Zvar (K4del, F5del, D6del, K7del, E8del, Q9A, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 91 VDA_____AQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I, A56del, P57del, K58del) SEQ ID NO: 92 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQ Zvar (V1del,, D2del, A3del, Q9A, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 93 ___KFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (V1del, D2del, A3del, K4del, F5del, D6del, K7del, E8del, Q9A, N11E, Q40V, A42K, N43A, L44I) SEQ ID NO: 94 ________AQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK Zvar (Q9A, N11E, Q40V, A42K, N43A, L441, K58_insYEDG) SEQ ID NO: 95 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKYE DG

In a second aspect the present invention discloses a multimer comprising, or consisting essentially of, a plurality of polypeptide units as defined by any embodiment disclosed above. The use of multimers may increase the immunoglobulin binding capacity and multimers may also have a higher alkali stability than monomers. The multimer can e.g. be a dimer, a trimer, a tetramer, a pentamer, a hexamer, a heptamer, an octamer or a nonamer. It can be a homomultimer, where all the units in the multimer are identical or it can be a heteromultimer, where at least one unit differs from the others. Advantageously, all the units in the multimer are alkali stable, such as by comprising the mutations disclosed above. The polypeptides can be linked to each other directly by peptide bonds between the C-terminal and N-terminal ends of the polypeptides. Alternatively, two or more units in the multimer can be linked by linkers comprising oligomeric or polymeric species, such as linkers comprising peptides with up to 25 or 30 amino acids, such as 3-25 or 3-20 amino acids. The linkers may e.g. comprise or consist essentially of a peptide sequence defined by, or having at least 90% identity or at least 95% identity, with an amino acid sequence selected from the group consisting of APKVDAKFDKE (SEQ ID NO:96), APKVDNKFNKE (SEQ ID NO:97), APKADNKFNKE (SEQ ID NO:98), APKVFDKE (SEQ ID NO:99), APAKFDKE (SEQ ID NO:100), AKFDKE (SEQ ID NO:101), APKVDA (SEQ ID NO:102), VDAKFDKE (SEQ ID NO:103), APKKFDKE (SEQ ID NO:104), APK, APKYEDGVDAKFDKE (SEQ ID NO:105) and YEDG (SEQ ID NO:106) or alternatively selected from the group consisting of APKADNKFNKE (SEQ ID NO:98), APKVFDKE (SEQ ID NO:99), APAKFDKE (SEQ ID NO:100), AKFDKE (SEQ ID NO:101), APKVDA (SEQ ID NO:102), VDAKFDKE (SEQ ID NO:103), APKKFDKE (SEQ ID NO:104), APKYEDGVDAKFDKE (SEQ ID NO:105) and YEDG (SEQ ID NO:106). They can also consist essentially of a peptide sequence defined by or having at least 90% identity or at least 95% identity with an amino acid sequence selected from the group consisting of APKADNKFNKE (SEQ ID NO:98), APKVFDKE (SEQ ID NO:99), APAKFDKE (SEQ ID NO:100), AKFDKE (SEQ ID NO:101), APKVDA (SEQ ID NO:102), VDAKFDKE (SEQ ID NO:103), APKKFDKE (SEQ ID NO:104), APK and APKYEDGVDAKFDKE (SEQ ID NO:105). In some embodiments the linkers do not consist of the peptides APKVDAKFDKE (SEQ ID NO:96) or APKVDNKFNKE (SEQ ID NO:97), or alternatively do not consist of the peptides APKVDAKFDKE (SEQ ID NO:96), APKVDNKFNKE (SEQ ID NO:97).

The nature of such a linker should preferably not destabilize the spatial conformation of the protein units. This can e.g. be achieved by avoiding the presence of proline in the linkers. Furthermore, said linker should preferably also be sufficiently stable in alkaline environments not to impair the properties of the mutated protein units. For this purpose, it is advantageous if the linkers do not contain asparagine. It can additionally be advantageous if the linkers do not contain glutamine. The multimer may further at the N-terminal end comprise a plurality of amino acid residues e.g. originating from the cloning process or constituting a residue from a cleaved off signaling sequence. The number of additional amino acid residues may e.g. be 20 or less, such as 15 or less, such as 10 or less or 5 or less. As a specific example, the multimer may comprise an AQ, AQGT (SEQ ID NO:107), VDAKFDKE (SEQ ID NO:103), AQVDAKFDKE (SEQ ID NO:108) or AQGTVDAKFDKE (SEQ ID NO:109) sequence at the N-terminal end.

In certain embodiments, the multimer may comprise, or consist essentially, of a sequence selected from the group consisting of: SEQ ID NO:80-87. These and additional sequences are listed below and named as Parent(Mutations)n, where n is the number of monomer units in a multimer.

Zvar (Q9A, N11E, N43A)4 SEQ ID NO: 17 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSQ SAALLAEAKK LNDAQAPKC Zvar (Q9A, N11E, N28A, N43A)4 SEQ ID NO: 18 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSQ SAALLAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSQ SAALLAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43E, L44I)4 SEQ ID NO: 19 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKEILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKEILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKEILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKEILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)4 SEQ ID NO: 20 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (NHK, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y)4 SEQ ID NO: 30 AQGT VDAKFDKEQQ KAFYEILKLP NLTEEQRNAF IQKLKDEPSQ SRAILAEAKR YNDAQAPK VDAKFDKEQQ KAFYEILKLP NLTEEQRNAF IQKLKDEPSQ SRAILAEAKR YNDAQAPK VDAKFDKEQQ KAFYEILKLP NLTEEQRNAF IQKLKDEPSQ SRAILAEAKR YNDAQAPK VDAKFDKEQQ KAFYEILKLP NLTEEQRNAF IQKLKDEPSQ SRAILAEAKR YNDAQAPKC Zvar (Q9A, NllK, H18K, D37E, A42R)4 SEQ ID NO: 31 AQGT VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRNLLAEAKK LNDAQAPK VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRNLLAEAKK LNDAQAPK VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRNLLAEAKK LNDAQAPK VDAKFDKEAQ KAFYEILKLP NLTEEQRNAF IQSLKDEPSQ SRNLLAEAKK LNDAQAPKC Zvar (Q9A, N11E, N28A, Q40V, A42K, N43A, L44I)4 SEQ ID NO: 32 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRAAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)6 SEQ ID NO: 33 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, D37E, Q40V, A42K, N43A, L44I)4 SEQ ID NO: 34 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, D37E, Q40V, A42R, N43A, L44I)4 SEQ ID NO: 35 AQGT VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SRAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SRAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SRAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDEPSV SRAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with D2, A3 and K4 in linker deleted SEQ ID NO: 80 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with K58, V1 and D2 in linker deleted SEQ ID NO: 81 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAP AKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with P57, K58, V1, D2 and A3 in linker deleted SEQ ID NO: 82 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK   LNDAQAP AKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with K4, F5, D6, K7 and E8 in linker deleted SEQ ID NO: 83 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with A56, P57 and K58 in linker deleted SEQ ID NO: 84 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQ VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with VI, D2 and A3 in linker deleted SEQ ID NO: 85 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK KFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with VI, D2, A3, K4, F5, D6, K7 and E8  in linker deleted SEQ ID NO: 86 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK AQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar (Q9A, N11E, Q40V, A42K, N43A, L44I)2 with YEDG inserted in linker between K58 and V1 SEQ ID NO: 87 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK YEDG VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC Zvar2 SEQ ID NO: 88 VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPK VDAKFDKEAQ EAFYEILHLP NLTEEQRNAF IQSLKDDPSV SKAILAEAKK LNDAQAPKC

In some embodiments, the polypeptide and/or multimer, as disclosed above, further comprises at the C-terminal or N-terminal end one or more coupling elements, selected from the group consisting of one or more cysteine residues, a plurality of lysine residues and a plurality of histidine residues. The coupling element(s) may also be located within 1-5 amino acid residues, such as within 1-3 or 1-2 amino acid residues from the C-terminal or N-terminal end. The coupling element may e.g. be a single cysteine at the C-terminal end. The coupling element(s) may be directly linked to the C- or N-terminal end, or it/they may be linked via a stretch comprising up to 15 amino acids, such as 1-5, 1-10 or 5-10 amino acids. This stretch should preferably also be sufficiently stable in alkaline environments not to impair the properties of the mutated protein. For this purpose, it is advantageous if the stretch does not contain asparagine. It can additionally be advantageous if the stretch does not contain glutamine. An advantage of having a C-terminal cysteine is that endpoint coupling of the protein can be achieved through reaction of the cysteine thiol with an electrophilic group on a support. This provides excellent mobility of the coupled protein which is important for the binding capacity.

The alkali stability of the polypeptide or multimer can be assessed by coupling it to an SPR chip, e.g. to Biacore CM5 sensor chips as described in the examples, using e.g. NHS- or maleimide coupling chemistries, and measuring the immunoglobulin-binding capacity of the chip, typically using polyclonal human IgG, before and after incubation in alkaline solutions at a specified temperature, e.g. 22+/−2° C. The incubation can e.g. be performed in 0.5 M NaOH for a number of 10 min cycles, such as 100, 200 or 300 cycles. The IgG capacity of the matrix after 100 10 min incubation cycles in 0.5 M NaOH at 22+/−2° C. can be at least 55, such as at least 60, at least 80 or at least 90% of the IgG capacity before the incubation. Alternatively, the remaining IgG capacity after 100 cycles for a particular mutant measured as above can be compared with the remaining IgG capacity for the parental polypeptide/multimer. In this case, the remaining IgG capacity for the mutant may be at least 105%, such as at least 110%, at least 125%, at least 150% or at least 200% of the parental polypeptide/multimer.

In a third aspect the present invention discloses a nucleic acid encoding a polypeptide or multimer according to any embodiment disclosed above. Thus, the invention encompasses all forms of the present nucleic acid sequence such as the RNA and the DNA encoding the polypeptide or multimer. The invention embraces a vector, such as a plasmid, which in addition to the coding sequence comprises the required signal sequences for expression of the polypeptide or multimer according the invention. In one embodiment, the vector comprises nucleic acid encoding a multimer according to the invention, wherein the separate nucleic acids encoding each unit may have homologous or heterologous DNA sequences.

In a fourth aspect the present invention discloses an expression system, which comprises, a nucleic acid or a vector as disclosed above. The expression system may e.g. be a gram-positive or gram-negative prokaryotic host cell system, e.g. E. coli or Bacillus sp. which has been modified to express the present polypeptide or multimer. In an alternative embodiment, the expression system is a eukaryotic host cell system, such as a yeast, e.g. Pichia pastoris or Saccharomyces cerevisiae, or mammalian cells, e.g. CHO cells.

In a fifth aspect, the present invention discloses a separation matrix, wherein a plurality of polypeptides or multimers according to any embodiment disclosed above have been coupled to a solid support. The separation matrix may comprise at least 11, such as 11-21, 15-21 or 15-18 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein:

a) the ligands comprise multimers of alkali-stabilized Protein A domains,

b) the porous support comprises cross-linked polymer particles having a volume-weighted median diameter (d50, v) of 56-70, such as 56-66, micrometers and a dry solids weight of 55-80, such as 60-78 or 65-78, mg/ml. The cross-linked polymer particles may further have a pore size corresponding to an inverse gel filtration chromatography Kd value of 0.69-0.85, such as 0.70-0.85 or 0.69-0.80, for dextran of Mw 110 kDa. Suitably, the cross-linked polymer particles can have a high rigidity, to be able to withstand high flow rates. The rigidity can be measured with a pressure-flow test as further described in Example 8, where a column packed with the matrix is subjected to increasing flow rates of distilled water. The pressure is increased stepwise and the flow rate and back pressure measured, until the flow rate starts to decrease with increasing pressures. The maximum flow rate achieved and the maximum pressure (the back pressure corresponding to the maximum flow rate) are measured and used as measures of the rigidity. When measured in a FINELINE 35 column (GE Healthcare Life Sciences) at a bed height of 300+/−10 mm, the max pressure can suitably be at least 0.58 MPa, such as at least 0.60 MPa. This allows for the use of smaller particle diameters, which is beneficial for the dynamic capacity. The multimers may e.g. comprise tetramers, pentamers, hexamers or heptamers of alkali-stabilized Protein A domains, such as hexamers of alkali-stabilized Protein A domains. The combination of the high ligand contents with the particle size range, the dry solids weight range and the optional Kd range provides for a high binding capacity, e.g. such that the 10% breakthrough dynamic binding capacity for IgG is at least 45 mg/ml, such as at least 50 or at least 55 mg/ml at 2.4 min residence time. Alternatively, or additionally, the 10% breakthrough dynamic binding capacity for IgG may be at least 60 mg/ml, such as at least 65, at least 70 or at least 75 mg/ml at 6 min residence time. The alkali-stabilized Protein A multimers are highly selective for IgG and the separation matrix can suitably have a dissociation constant for human IgG2 of below 0.2 mg/ml, such as below 0.1 mg/ml, in 20 mM phosphate buffer, 180 mM NaCl, pH 7.5. This can be determined according to the adsorption isotherm method described in N Pakiman et al: J Appl Sci 12, 1136-1141 (2012).

In certain embodiments the alkali-stabilized Protein A domains comprise mutants of a parental Fc-binding domain of Staphylococcus Protein A (SpA), as defined by, or having at least 80% such as at least 90%, 95% or 98% identity to, SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO:3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:22, SEQ ID NO:51 or SEQ ID NO:52, wherein at least the asparagine or serine residue at the position corresponding to position 11 in SEQ ID NO:4-7 has been mutated to an amino acid selected from the group consisting of glutamic acid, lysine, tyrosine, threonine, phenylalanine, leucine, isoleucine, tryptophan, methionine, valine, alanine, histidine and arginine, such as an amino acid selected from the group consisting of glutamic acid and lysine. The amino acid residue at the position corresponding to position 40 in SEQ ID NO:4-7 may further be, or be mutated to, a valine. The alkali-stabilized Protein A domains may also comprise any mutations as described in the polypeptide and/or multimer embodiments above.

In some embodiments the alkali-stabilized Protein A domains comprise an Fc-binding polypeptide having an amino acid sequence as defined by, or having at least 80% or at least 90, 95% or 98% identity to SEQ ID NO:53.

 (SEQ ID NO: 53) X₁Q X₂AFYEILX₃LP NLTEEQRX₄X₅F IX₆X₇LKDX₈PSX₉ SX₁₀X₁₁X₁₂LAEAKX₁₃ X₁₄NX₁₅AQ wherein individually of each other: X₁=A or Q or is deleted X₂=E, K, Y, T, F, L, W, I, M, V, A, H or R X₃=H or K X₄=A or N X₅=A, G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K X₆=Q or E X₇=S or K X₈=E or D X₉=Q or V or is deleted X₁₀=K, R or A or is deleted X₁₁=A, E or N or is deleted X₁₂=I or L X₁₃=K or R X₁₄=L or Y X₁₅=D, F, Y, W, K or R

In some embodiments, the amino acid residues may individually of each other be:

a) X₁=A or is deleted, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V or is deleted, X₁₀=K or is deleted, X₁₁=A or is deleted, X₁₂=I, X₁₃=K, X₁₄=L.

b) X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D.

c) X₁ is A, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D or

d) X₁ is A, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D.

In certain embodiments the invention discloses a separation matrix comprising at least 15, such as 15-21 or 15-18 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein the ligands comprise multimers of alkali-stabilized Protein A domains. These multimers can suitably be as disclosed in any of the embodiments described above or as specified below.

Such a matrix is useful for separation of immunoglobulins or other Fc-containing proteins and, due to the improved alkali stability of the polypeptides/multimers, the matrix will withstand highly alkaline conditions during cleaning, which is essential for long-term repeated use in a bioprocess separation setting. The alkali stability of the matrix can be assessed by measuring the immunoglobulin-binding capacity, typically using polyclonal human IgG, before and after incubation in alkaline solutions at a specified temperature, e.g. 22+/−2° C. The incubation can e.g. be performed in 0.5 M or 1.0 M NaOH for a number of 15 min cycles, such as 100, 200 or 300 cycles, corresponding to a total incubation time of 25, 50 or 75 h. The IgG capacity of the matrix after 96-100 15 min incubation cycles or a total incubation time of 24 or 25 h in 0.5 M NaOH at 22+/−2° C. can be at least 80, such as at least 85, at least 90 or at least 95% of the IgG capacity before the incubation. The capacity of the matrix after a total incubation time of 24 h in 1.0 M NaOH at 22+/−2° C. can be at least 70, such as at least 80 or at least 90% of the IgG capacity before the incubation. The 10% breakthrough dynamic binding capacity (Qb10%) for IgG at 2.4 min or 6 min residence time may e.g. be reduced by less than 20% after incubation 31 h in 1.0 M aqueous NaOH at 22+/−2 C.

As the skilled person will understand, the expressed polypeptide or multimer should be purified to an appropriate extent before being immobilized to a support. Such purification methods are well known in the field, and the immobilization of protein-based ligands to supports is easily carried out using standard methods. Suitable methods and supports will be discussed below in more detail.

The solid support of the matrix according to the invention can be of any suitable well-known kind. A conventional affinity separation matrix is often of organic nature and based on polymers that expose a hydrophilic surface to the aqueous media used, i.e. expose hydroxy (—OH), carboxy (—COOH), carboxamido (—CONH₂, possibly in N— substituted forms), amiNO:(—NH₂, possibly in substituted form), oligo- or polyethylenoxy groups on their external and, if present, also on internal surfaces. The solid support can suitably be porous. The porosity can be expressed as a Kav or Kd value (the fraction of the pore volume available to a probe molecule of a particular size) measured by inverse size exclusion chromatography, e.g. according to the methods described in Gel Filtration Principles and Methods, Pharmacia LKB Biotechnology 1991, pp 6-13. Kav is determined as the ratio (V_(e)−V₀)/(V_(t)−V₀), where V_(e) is the elution volume of a probe molecule (e.g. Dextran 110 kD), V₀ is the void volume of the column (e.g. the elution volume of a high Mw void marker, such as raw dextran) and V_(t) is the total volume of the column. Kd can be determined as (V_(e)−V₀)/V_(i), where V_(i) is the elution volume of a salt (e.g. NaCl) able to access all the volume except the matrix volume (the volume occupied by the matrix polymer molecules). By definition, both Kd and Kav values always lie within the range 0-1. The Kav value can advantageously be 0.6-0.95, e.g. 0.7-0.90 or 0.6-0.8, as measured with dextran of Mw 110 kDa as a probe molecule. The Kd value as measured with dextran of Mw 110 kDa can suitably be 0.68-0.90, such as 0.68-0.85 or 0.70-0.85. An advantage of this is that the support has a large fraction of pores able to accommodate both the polypeptides/multimers of the invention and immunoglobulins binding to the polypeptides/multimers and to provide mass transport of the immunoglobulins to and from the binding sites.

The polypeptides or multimers may be attached to the support via conventional coupling techniques utilising e.g. thiol, amiNO: and/or carboxy groups present in the ligand. Bisepoxides, epichlorohydrin, CNBr, N-hydroxysuccinimide (NHS) etc are well-known coupling reagents. Between the support and the polypeptide/multimer, a molecule known as a spacer can be introduced, which improves the availability of the polypeptide/multimer and facilitates the chemical coupling of the polypeptide/multimer to the support. Depending on the nature of the polypeptide/multimer and the coupling conditions, the coupling may be a multipoint coupling (e.g. via a plurality of lysines) or a single point coupling (e.g. via a single cysteine). Alternatively, the polypeptide/multimer may be attached to the support by non-covalent bonding, such as physical adsorption or biospecific adsorption.

In some embodiments the matrix comprises 5-25, such as 5-20 mg/ml, 5-15 mg/ml, 5-11 mg/ml or 6-11 mg/ml of the polypeptide or multimer coupled to the support. The amount of coupled polypeptide/multimer can be controlled by the concentration of polypeptide/multimer used in the coupling process, by the activation and coupling conditions used and/or by the pore structure of the support used. As a general rule the absolute binding capacity of the matrix increases with the amount of coupled polypeptide/multimer, at least up to a point where the pores become significantly constricted by the coupled polypeptide/multimer. Without being bound by theory, it appears though that for the Kd values recited for the support, the constriction of the pores by coupled ligand is of lower significance. The relative binding capacity per mg coupled polypeptide/multimer will decrease at high coupling levels, resulting in a cost-benefit optimum within the ranges specified above.

In certain embodiments the polypeptides or multimers are coupled to the support via thioether bonds. Methods for performing such coupling are well-known in this field and easily performed by the skilled person in this field using standard techniques and equipment. Thioether bonds are flexible and stable and generally suited for use in affinity chromatography. In particular when the thioether bond is via a terminal or near-terminal cysteine residue on the polypeptide or multimer, the mobility of the coupled polypeptide/multimer is enhanced which provides improved binding capacity and binding kinetics. In some embodiments the polypeptide/multimer is coupled via a C-terminal cysteine provided on the protein as described above. This allows for efficient coupling of the cysteine thiol to electrophilic groups, e.g. epoxide groups, halohydrin groups etc. on a support, resulting in a thioether bridge coupling.

In certain embodiments the support comprises a polyhydroxy polymer, such as a polysaccharide. Examples of polysaccharides include e.g. dextran, starch, cellulose, pullulan, agar, agarose etc. Polysaccharides are inherently hydrophilic with low degrees of nonspecific interactions, they provide a high content of reactive (activatable) hydroxyl groups and they are generally stable towards alkaline cleaning solutions used in bioprocessing.

In some embodiments the support comprises agar or agarose. The supports used in the present invention can easily be prepared according to standard methods, such as inverse suspension gelation (S Hjertén: Biochim Biophys Acta 79(2), 393-398 (1964). Alternatively, the base matrices are commercially available products, such as crosslinked agarose beads sold under the name of SEPHAROSE™ FF (GE Healthcare). In an embodiment, which is especially advantageous for large-scale separations, the support has been adapted to increase its rigidity using the methods described in U.S. Pat. No. 6,602,990 or 7,396,467, which are hereby incorporated by reference in their entireties, and hence renders the matrix more suitable for high flow rates.

In certain embodiments the support, such as a polymer, polysaccharide or agarose support, is crosslinked, such as with hydroxyalkyl ether crosslinks. Crosslinker reagents producing such crosslinks can be e.g. epihalohydrins like epichlorohydrin, diepoxides like butanediol diglycidyl ether, allylating reagents like allyl halides or allyl glycidyl ether. Crosslinking is beneficial for the rigidity of the support and improves the chemical stability. Hydroxyalkyl ether crosslinks are alkali stable and do not cause significant nonspecific adsorption.

Alternatively, the solid support is based on synthetic polymers, such as polyvinyl alcohol, polyhydroxyalkyl acrylates, polyhydroxyalkyl methacrylates, polyacrylamides, polymethacrylamides etc. In case of hydrophobic polymers, such as matrices based on divinyl and monovinyl-substituted benzenes, the surface of the matrix is often hydrophilised to expose hydrophilic groups as defined above to a surrounding aqueous liquid. Such polymers are easily produced according to standard methods, see e.g. “Styrene based polymer supports developed by suspension polymerization” (R Arshady: Chimica e L'Industria 70(9), 70-75 (1988)). Alternatively, a commercially available product, such as SOURCE™ (GE Healthcare) is used. In another alternative, the solid support according to the invention comprises a support of inorganic nature, e.g. silica, zirconium oxide etc.

In yet another embodiment, the solid support is in another form such as a surface, a chip, capillaries, or a filter (e.g. a membrane or a depth filter matrix).

As regards the shape of the matrix according to the invention, in one embodiment the matrix is in the form of a porous monolith. In an alternative embodiment, the matrix is in beaded or particle form that can be porous or non-porous. Matrices in beaded or particle form can be used as a packed bed or in a suspended form. Suspended forms include those known as expanded beds and pure suspensions, in which the particles or beads are free to move. In case of monoliths, packed bed and expanded beds, the separation procedure commonly follows conventional chromatography with a concentration gradient. In case of pure suspension, batch-wise mode will be used.

In a sixth aspect, the present invention discloses a method of isolating an immunoglobulin, wherein a separation matrix as disclosed above is used. The method may comprise the steps of:

a) contacting a liquid sample comprising an immunoglobulin with a separation matrix as disclosed above,

b) washing the separation matrix with a washing liquid,

c) eluting the immunoglobulin from the separation matrix with an elution liquid, and

d) cleaning the separation matrix with a cleaning liquid, which may comprise 0.1-1.0 M NaOH or KOH, such as 0.4-1.0 M NaOH or KOH.

Steps a)-d) may be repeated at least 10 times, such as at least 50 times or 50-200 times.

In certain embodiments, the method comprises the steps of:

a) contacting a liquid sample comprising an immunoglobulin with a separation matrix as disclosed above,

b) washing said separation matrix with a washing liquid,

c) eluting the immunoglobulin from the separation matrix with an elution liquid, and

d) cleaning the separation matrix with a cleaning liquid, which can alternatively be called a cleaning-in-place (CIP) liquid, e.g. with a contact (incubation) time of at least 10 min.

The method may also comprise steps of, before step a), providing an affinity separation matrix according to any of the embodiments described above and providing a solution comprising an immunoglobulin and at least one other substance as a liquid sample and of, after step c), recovering the eluate and optionally subjecting the eluate to further separation steps, e.g. by anion or cation exchange chromatography, multimodal chromatography and/or hydrophobic interaction chromatography. Suitable compositions of the liquid sample, the washing liquid and the elution liquid, as well as the general conditions for performing the separation are well known in the art of affinity chromatography and in particular in the art of Protein A chromatography. The liquid sample comprising an Fc-containing protein and at least one other substance may comprise host cell proteins (HCP), such as CHO cell, E Coli or yeast proteins. Contents of CHO cell and E Coli proteins can conveniently be determined by immunoassays directed towards these proteins, e.g. the CHO HCP or E Coli HCP ELISA kits from Cygnus Technologies. The host cell proteins or CHO cell/E Coli proteins may be desorbed during step b).

The elution may be performed by using any suitable solution used for elution from Protein A media. This can e.g. be a solution or buffer with pH 5 or lower, such as pH 2.5-5 or 3-5. It can also in some cases be a solution or buffer with pH 11 or higher, such as pH 11-14 or pH 11-13. In some embodiments the elution buffer or the elution buffer gradient comprises at least one mono- di- or trifunctional carboxylic acid or salt of such a carboxylic acid. In certain embodiments the elution buffer or the elution buffer gradient comprises at least one anion species selected from the group consisting of acetate, citrate, glycine, succinate, phosphate, and formiate.

In some embodiments, the cleaning liquid is alkaline, such as with a pH of 13-14. Such solutions provide efficient cleaning of the matrix, in particular at the upper end of the interval

In certain embodiments, the cleaning liquid comprises 0.1-2.0 M NaOH or KOH, such as 0.5-2.0 or 0.5-1.0 M NaOH or KOH. These are efficient cleaning solutions, and in particular so when the NaOH or KOH concentration is above 0.1 M or at least 0.5 M. The high stability of the polypeptides of the invention enables the use of such strongly alkaline solutions.

The method may also include a step of sanitizing the matrix with a sanitization liquid, which may e.g. comprise a peroxide, such as hydrogen peroxide and/or a peracid, such as peracetic acid or performic acid.

In some embodiments, steps a)-d) are repeated at least 10 times, such as at least 50 times, 50-200, 50-300 or 50-500 times. This is important for the process economy in that the matrix can be re-used many times.

Steps a)-c) can also be repeated at least 10 times, such as at least 50 times, 50-200, 50-300 or 50-500 times, with step d) being performed after a plurality of instances of step c), such that step d) is performed at least 10 times, such as at least 50 times. Step d) can e.g. be performed every second to twentieth instance of step c).

EXAMPLES

Mutagenesis of Protein

Site-directed mutagenesis was performed by a two-step PCR using oligonucleotides coding for the mutations. As template a plasmid containing a single domain of either Z, B or C was used. The PCR fragments were ligated into an E. coli expression vector. DNA sequencing was used to verify the correct sequence of inserted fragments.

To form multimers of mutants an Acc I site located in the starting codons (GTA GAC) of the B, C or Z domain was used, corresponding to amino acids VD. The vector for the monomeric domain was digested with Acc I and phosphatase treated. Acc I sticky-ends primers were designed, specific for each variant, and two overlapping PCR products were generated from each template. The PCR products were purified and the concentration was estimated by comparing the PCR products on a 2% agarose gel. Equal amounts of the pair wise PCR products were hybridized (90° C.→25° C. in 45 min) in ligation buffer. The resulting product consists approximately to ¼ of fragments likely to be ligated into an Acc I site (correct PCR fragments and/or the digested vector). After ligation and transformation colonies were PCR screened to identify constructs containing the desired mutant. Positive clones were verified by DNA sequencing. Construct Expression and Purification

The constructs were expressed in the bacterial periplasm by fermentation of E. coli K12 in standard media. After fermentation the cells were heat-treated to release the periplasm content into the media. The constructs released into the medium were recovered by microfiltration with a membrane having a 0.2 μm pore size.

Each construct, now in the permeate from the filtration step, was purified by affinity. The permeate was loaded onto a chromatography medium containing immobilized IgG (IgG Sepharose 6FF, GE Healthcare). The loaded product was washed with phosphate buffered saline and eluted by lowering the pH.

The elution pool was adjusted to a neutral pH (pH 8) and reduced by addition of dithiothreitol. The sample was then loaded onto an anion exchanger. After a wash step the construct was eluted in a NaCl gradient to separate it from any contaminants. The elution pool was concentrated by ultrafiltration to 40-50 mg/ml. It should be noted that the successful affinity purification of a construct on an immobilized IgG medium indicates that the construct in question has a high affinity to IgG.

The purified ligands were analyzed with RPC LC-MS to determine the purity and to ascertain that the molecular weight corresponded to the expected (based on the amino acid sequence).

Example 1

The purified monomeric ligands listed in Table 1, further comprising for SEQ ID NO:8-16, 23-28 and 36-48 an AQGT leader sequence at the N-terminus and a cysteine at the C terminus, were immobilized on Biacore CM5 sensor chips (GE Healthcare, Sweden), using the amine coupling kit of GE Healthcare (for carbodiimide coupling of amines on the carboxymethyl groups on the chip) in an amount sufficient to give a signal strength of about 200-1500 RU in a Biacore surface plasmon resonance (SPR) instrument (GE Healthcare, Sweden). To follow the IgG binding capacity of the immobilized surface 1 mg/ml human polyclonal IgG (Gammanorm) was flowed over the chip and the signal strength (proportional to the amount of binding) was noted. The surface was then cleaned-in-place (CIP), i.e. flushed with 500 mM NaOH for 10 minutes at room temperature (22+/−2° C.). This was repeated for 96-100 cycles and the immobilized ligand alkaline stability was followed as the remaining IgG binding capacity (signal strength) after each cycle. The results are shown in Table 1 and indicate that at least the ligands Zvar(N11K)1, Zvar(N11E)1, Zvar(N11Y)1, Zvar(N11T)1, Zvar(N11F)1, Zvar(N11L)1, Zvar(N11W)1, ZN11I)1, Zvar(N11M)1, Zvar(N11V)1, Zvar(N11A)1, Zvar(N11H1), Zvar(N11R)1, Zvar(N11E, Q32A)1, Zvar(N11E, Q32E, Q40E)1 and Zvar(N11E, Q32E, K50R)1, Zvar(Q9A, N11E, N43A)1, Zvar(Q9A, N11E, N28A, N43A)1, Zvar(Q9A, N11E, Q40V, A42K, N43E, L44I)1, Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)1, Zvar(Q9A, N11E, N28A, Q40V, A42K, N43A, L44I)1, Zvar(N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y)1, Zvar(Q9A, N11K, H18K, S33K, D37E, A42R, N43A, L44I, K50R, L51Y)1, Zvar(N11K, H18K, D37E, A42R, N43A, L44I)1, Zvar(Q9A, N11K, H18K, D37E, A42R, N43A, L44I)1 and Zvar(Q9A, N11K, H18K, D37E, A42R, N43A, L44I, K50R)1, as well as the varieties of Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)1 having G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K in position 29, the varieties of Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)1 having F, Y, W, K or R in position 53 and the varieties of Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)1 where Q9, Q40, A42 or N43 has been deleted, have an improved alkali stability compared to the parental structure Zvar1, used as the reference. Further, the ligands B(Q9A, N11E, Q40V, A42K, N43A, L44I)1 and C(Q9A, N11E, E43A)1 have an improved stability compared to the parental B and C domains, used as references.

TABLE 1 Monomeric ligands, evaluated by Biacore (0.5M NaOH). Capacity Reference Capacity after 96- capacity relative 100 after 96- to Ligand Sequence cycles 100 cycles reference Zvar(N11E, Q32A)1 SEQ ID 57% 55% 1.036 NO: 12 Zvar(N11E)1 SEQ ID 59% 55% 1.073 NO: 13 Zvar(N11E, Q32E, Q40E)1 SEQ ID 52% 51% 1.020 NO: 14 Zvar(N11E, Q32E, K50R)1 SEQ ID 53% 51% 1.039 NO: 15 Zvar(N11K)1 SEQI D 62% 49% 1.270 NO: 16 Zvar(N11Y)1 SEQ ID 55% 46% 1.20 NO: 38 Zvar(N11T)1 SEQ ID 50% 46% 1.09 NO: 39 Zvar(N11F)1 SEQ ID 55% 46% 1.20 NO: 40 Zvar(N11L)1 SEQ ID 57% 47% 1.21 NO: 41 Zvar(N11W)1 SEQ ID 57% 47% 1.21 NO: 42 Zvar(N11I)1 SEQ ID 57% 47% 1.21 NO: 43 Zvar(N11M)1 SEQ ID 58% 46% 1.26 NO: 44 Zvar(N11V)1 SEQ ID 56% 46% 1.22 NO: 45 Zvar(N11A)1 SEQ ID 58% 46% 1.26 NO: 46 Zvar(N11H)1 SEQ ID 57% 46% 1.24 NO: 47 Zvar(N11R)1 SEQ ID 59% 46% 1.28 NO: 48 Zvar(Q9A, N11E, N43A)1 SEQ ID 70% 47% 1.49 NO: 8 Zvar(Q9A, N11E, N28A, N43A)1 SEQ ID 68% 47% 1.45 NO: 9 Zvar(Q9A, N11E, Q40V, A42K, SEQ ID 67% 47% 1.43 N43E, L44I)1 NO: 10 Zvar(Q9A, N11E, Q40V, A42K, SEQ ID 66% 47% 1.40 N43A, L44I)1 NO: 11 Zvar(Q9A, N11E, N28A, Q40V, SEQ ID 65% 48% 1.35 A42K, N43A, L44I)1 NO: 24 Zvar(N11K, H18K, S33K, D37E, SEQ ID 67% 46% 1.46 A42R, N43A, L44I, K50R, L51Y)1 NO: 23 Zvar(Q9A, N11K, H18K, S33K, D37E, SEQ ID 59% 46% 1.28 A42R, N43A, L44I, K50R, L51Y)1 NO: 25 Zvar(N11K, H18K, D37E, A42R, N43A, SEQ ID 59% 45% 1.31 L44I)1 NO: 26 Zvar(Q9A, N11K, H18K, D37E, A42R, SEQ ID 63% 45% 1.40 N43A, L44I)1 NO: 27 Zvar(Q9A, N11K, H18K, D37E, A42R, SEQ ID 67% 45% 1.49 N43A, L44I, K50R)1 NO: 28 B(Q9A, N11E, Q40V, A42K, N43A, SEQ ID 39% 35% 1.11 L44I)1 NO: 36 C(Q9A, N11E, E43A)1 SEQ ID 60% 49% 1.22 NO: 37 Zvar(Q9A, N11E, A29G, Q40V, A42K, SEQ ID 69% 48% 1.44 N43A, L44I)1 NO: 54 Zvar(Q9A, N11E, A29S, Q40V, A42K, SEQ ID 66% 48% 1.38 N43A, L44I)1 NO: 55 Zvar(Q9A, N11E, A29Y, Q40V, A42K, SEQ ID 61% 48% 1.27 N43A, L44I)1 NO: 56 Zvar(Q9A, N11E, A29Q, Q40V, A42K, SEQ ID 60% 47% 1.28 N43A, L44I)1 NO: 57 Zvar(Q9A, N11E, A29T, Q40V, A42K, SEQ ID 60% 47% 1.28 N43A, L44I)1 NO: 58 Zvar(Q9A, N11E, A29N, Q40V, A42K, SEQ ID 61% 47% 1.30 N43A, L44I)1 NO: 59 Zvar(Q9A, N11E, A29F, Q40V, A42K, SEQ ID 62% 46% 1.35 N43A, L44I)1 NO: 60 Zvar(Q9A, N11E, A29L, Q40V, A42K, SEQ ID 61% 46% 1.33 N43A, L44I)1 NO: 61 Zvar(Q9A, N11E, A29W, Q40V, A42K, SEQ ID 60% 46% 1.30 N43A, L44I)1 NO: 62 Zvar(Q9A, N11E, A29I, Q40V, A42K, SEQ ID 58% 47% 1.23 N43A, L44I)1 NO: 63 Zvar(Q9A, N11E, A29M, Q40V, A42K, SEQ ID 62% 47% 1.32 N43A, L44I)1 NO: 64 Zvar(Q9A, N11E, A29V, Q40V, A42K, SEQ ID 62% 47% 1.32 N43A, L44I)1 NO: 65 Zvar(Q9A, N11E, A29D, Q40V, A42K, SEQ ID 56% 47% 1.19 N43A, L44I)1 NO: 66 Zvar(Q9A, N11E, A29E, Q40V, A42K, SEQ ID 57% 47% 1.21 N43A, L44I)1 NO: 67 Zvar(Q9A, N11E, A29H, Q40V, A42K, SEQ ID 57% 47% 1.21 N43A, L44I)1 NO: 68 Zvar(Q9A, N11E, A29R, Q40V, A42K, SEQ ID 58% 46% 1.26 N43A, L44I)1 NO: 69 Zvar(Q9A, N11E, A29K, Q40V, A42K, SEQ ID 59% 46% 1.28 N43A, L44I)1 NO: 70 Zvar(Q9A, N11E, Q40V, A42K, N43A, SEQ ID 58% 46% 1.26 L44I, D53F)1 NO: 71 Zvar(Q9A, N11E, Q40V, A42K, N43A, SEQ ID 59% 46% 1.28 L44I, D53Y)1 NO: 72 Zvar(Q9A, N11E, Q40V, A42K, N43A, SEQ ID 62% 46% 1.35 L44I, D53W)1 NO: 73 Zvar(Q9A, N11E, Q40V, A42K, N43A, SEQ ID 65% 46% 1.41 L44I, D53K)1 NO: 74 Zvar(Q9A, N11E, Q40V, A42K, N43A, SEQ ID 60% 46% 1.30 L44I, D53R)1 NO: 75 Zvar(Q9del, N11E, Q40V, A42K, N43A, SEQ ID 60% 46% 1.30 L44I)1 NO: 76 Zvar(Q9A, N11E, Q40del, A42K, N43A, SEQ ID 59% 46% 1.28 L44I)1 NO: 77 Zvar(Q9A, N11E, Q40V, A42del, N43A, SEQ ID 57% 46% 1.24 L44I)1 NO: 78 Zvar(Q9A, N11E, Q40V, A42K, N43del, SEQ ID 55% 46% 1.20 L44I)1 NO: 79

The Biacore experiment can also be used to determine the binding and dissociation rates between the ligand and IgG. This was used with the set-up as described above and with an IgG1 monoclonal antibody as probe molecule. For the reference Zvar1, the on-rate (10⁵ M⁻¹s⁻¹) was 3.1 and the off-rate (10⁵ s⁻¹) was 22.1, giving an affinity (off-rate/on-rate) of 713 pM. For Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)1 (SEQ ID NO:11), the on-rate was 4.1 and the off-rate 43.7, with affinity 1070 pM. The IgG affinity was thus somewhat higher for the mutated variant.

Example 2

The purified dimeric, tetrameric and hexameric ligands listed in Table 2 were immobilized on Biacore CM5 sensor chips (GE Healthcare, Sweden), using the amine coupling kit of GE Healthcare (for carbodiimide coupling of amines on the carboxymethyl groups on the chip) in an amount sufficient to give a signal strength of about 200-1500 RU in a Biacore instrument (GE Healthcare, Sweden). To follow the IgG binding capacity of the immobilized surface 1 mg/ml human polyclonal IgG (Gammanorm) was flowed over the chip and the signal strength (proportional to the amount of binding) was noted. The surface was then cleaned-in-place (CIP), i.e. flushed with 500 mM NaOH for 10 minutes at room temperature (22+/−2° C.). This was repeated for 300 cycles and the immobilized ligand alkaline stability was followed as the remaining IgG binding capacity (signal strength) after each cycle. The results are shown in Table 2 and in FIG. 2 and indicate that at least the ligands Zvar(Q9A, N11E, N43A)4, Zvar(Q9A, N11E, N28A, N43A)4, Zvar(Q9A, N11E, Q40V, A42K, N43E, L44I)4 and Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)4, Zvar(Q9A, N11E, D37E, Q40V, A42K, N43A, L44I)4 and Zvar(Q9A, N11E, D37E, Q40V, A42R, N43A, L44I)4 have an improved alkali stability compared to the parental structure Zvar4, which was used as a reference. The hexameric ligand Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I)6 also has improved alkali stability compared to the parental structure Zvar6, used as a reference. Further, Zvar(Q9A, N11E, Q40V, A42K, N43A, L44I) dimers with deletions of a) D2, A3, K4; b) K58, V1, D2; c) P57, K58, V1, D2, A3; d) K4, F5, D6, K7, E8; e) A56, P57, K58; V1, D2, A3 or f) V1, D2, A3, K4, F5, D6, K7, E8 from the linker region between the two monomer units have improved alkali stability compared to the parental structure Zvar2, used as a reference. Also Zvar(Q9A, N11E, Q4V, A42K, N43A, L44I) dimers with an insertion of YEDG between K58 and V1 in the linker region have improved alkali stability compared to Zvar2.

TABLE 2 Dimeric, tetrameric and hexameric ligands, evaluated by Biacore (0.5M NaOH). Capacity Capacity Capacity Remaining relative Remaining relative Remaining relative SEQ capacity to ref. capacity to ref. capacity to ref. ID 100 cycles 100 200 cycles 200 300 cycles 300 Ligand NO: (%) cycles (%) cycles (%) cycles Zvar4 21 67 1 36 1 16 1 Zvar(Q9A, N11E, N43A)4 17 81 1.21 62 1.72 41 2.56 Zvar(Q9A, N11E, N28A, 18 80 1.19 62 1.72 42 2.62 N43A)4 Zvar(Q9A, N11E, Q40V, 19 84 1.25 65 1.81 48 3.00 A42K, N43E, L44I)4 Zvar(Q9A, N11E, Q40V, 20 90 1.34 74 2.06 57 3.56 A42K, N43A, L44I)4 Zvar(Q9A, N11E, N28A, 32 84 1.24 Not tested Not Not tested Not Q40V, A42K, N43A, L44I)4 tested tested Zvar(Q9A, N11E, Q40V, 33 87 1.30 Not tested Not Not tested Not A42K, N43A, L44I)6 tested tested Zvar(Q9A, N11E, D37E, 34 81 1.13 Not tested Not Not tested Not Q40V, A42K, N43A, L44I)4 tested tested Zvar(Q9A, N11E, D37E, 35 84 1.17 Not tested Not Not tested Not Q40V, A42R, N43A, L44I)4 tested tested Zvar(Q9A, N11E, Q40V, 80 70 1.27 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested D2, A3 and K4 in linker deleted Zvar(Q9A, N11E, Q40V, 81 76 1.38 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested K58, V1 and D2 in linker deleted Zvar(Q9A, N11E, Q40V, 82 74 1.35 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested P57, K58, V1, D2 and A3 in linker deleted Zvar(Q9A, N11E, Q40V, 83 70 1.30 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested K4, F5, D6, K7 and E8 in linker deleted Zvar(Q9A, N11E, Q40V, 84 68 1.26 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested A56, P57 and K58 in linker deleted Zvar(Q9A, N11E, Q40V, 85 75 1.39 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested V1, D2 and A3 in linker deleted Zvar(Q9A, N11E, Q40V, 86 62 1.13 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested V1, D2, A3, K4, F5, D6, K7 and E8 in linker deleted Zvar(Q9A, N11E, Q40V, 87 72 1.31 Not tested Not Not tested Not A42K, N43A, L44I)2 with tested tested YEDG inserted in linker between K58 and V1 Zvar2 88 55 1 Not tested Not Not tested Not tested tested

Example 3

Example 2 was repeated with 100 CIP cycles of three ligands using 1 M NaOH instead of 500 mM as in Example 2. The results are shown in Table 3 and show that all three ligands have an improved alkali stability also in 1M NaOH, compared to the parental structure Zvar4 which was used as a reference.

TABLE 3 Tetrameric ligands, evaluated by Biacore (1M NaOH). Remaining Capacity capacity 100 relative to Ligand Sequence cycles (%) ref. 100 cycles Zvar4 SEQ ID 27 1 NO: 21 Zvar(Q9A, N11E, N28A, SEQ ID 55 2.04 N43A)4 NO: 18 Zvar(Q9A, N11E, Q40V, SEQ ID 54 2.00 A42K, N43E, L44I)4 NO: 19 Zvar(Q9A, N11E, Q40V, SEQ ID 56 2.07 A42K, N43A, L44I)4 NO: 20

Example 4

The purified tetrameric ligands of Table 2 (all with an additional N-terminal cysteine) were immobilized on agarose beads using the methods described below and assessed for capacity and stability. The results are shown in Table 4 and FIG. 3 .

TABLE 4 Matrices with tetrametric ligands, evaluated in columns (0.5M NaOH). Remaining Capacity IgG Remaining retention Initial capacity IgG relative IgG Qb10 capacity to ref. SEQ Ligand capacity after six 4 after six 4 after ID content Qb10 h cycles h cycles six 4 h Ligand NO. (mg/ml) (mg/ml) (mg/ml) (%) cycles Zvar4 21 7 52.5 36.5 60 1 Zvar4 21 12 61.1 43.4 71 1 Zvar(Q9A, N11E, N28A, N43A)4 18 7.0 49.1 44.1 90 1.50 Zvar(Q9A, N11E, N28A, N43A)4 18 12.1 50.0 46.2 93 1.31 Zvar(Q9A, N11E, Q40V, A42K, 20 7.2 49.0 44.2 90 1.50 N43A, L44I)4 Zvar(Q9A, N11E, Q40V, A42K, 20 12.8 56.3 53.6 95 1.34 N43A, L44I)4 Zvar(N11K, H18K, S33K, D37E, 30 9.7 56.3 52.0 92 1.53 A42R, N43A, L44I, K50R, L51Y)4 Zvar(Q9A, N11K, H18K, D37E, 31 10.8 56.9 52.5 92 1.30 A42R)4 Activation

The base matrix used was rigid cross-linked agarose beads of 85 micrometers (volume-weighted, d50V) median diameter, prepared according to the methods of U.S. Pat. No. 6,602,990, hereby incorporated by reference in its entirety, and with a pore size corresponding to an inverse gel filtration chromatography Kay value of 0.70 for dextran of Mw 110 kDa, according to the methods described in Gel Filtration Principles and Methods, Pharmacia LKB Biotechnology 1991, pp 6-13.

25 mL (g) of drained base matrix, 10.0 mL distilled water and 2.02 g NaOH (s) was mixed in a 100 mL flask with mechanical stirring for 10 min at 25° C. 4.0 mL of epichlorohydrin was added and the reaction progressed for 2 hours. The activated gel was washed with 10 gel sediment volumes (GV) of water.

Coupling

To 20 mL of ligand solution (50 mg/mL) in a 50 ml Falcon tube, 169 mg NaHCO₃, 21 mg Na₂CO₃, 175 mg NaCl and 7 mg EDTA, was added. The Falcon tube was placed on a roller table for 5-10 min, and then 77 mg of DTE was added. Reduction proceeded for >45 min. The ligand solution was then desalted on a PD10 column packed with Sephadex G-25. The ligand content in the desalted solution was determined by measuring the 276 nm UV absorption.

The activated gel was washed with 3-5 GV 10.1 M phosphate/1 mM EDTA pH 8.61 and the ligand was then coupled according to the method described in U.S. Pat. No. 6,399,750, hereby incorporated by reference in its entirety. All buffers used in the experiments had been degassed by nitrogen gas for at least 5-10 min. The ligand content of the gels could be controlled by varying the amount and concentration of the ligand solution.

After immobilization the gels were washed 3×GV with distilled water. The gels+1 GV {0.1 M phosphate/1 mM EDTA/10% thioglycerol pH 8.6} was mixed and the tubes were left in a shaking table at room temperature overnight. The gels were then washed alternately with 3×GV {0.1 M TRIS/0.15 M NaCl pH 8.6} and 0.5 M HAc and then 8-10×GV with distilled water. Gel samples were sent to an external laboratory for amino acid analysis and the ligand content (mg/ml gel) was calculated from the total amino acid content.

Protein

Gammanorm 165 mg/ml (Octapharma), diluted to 2 mg/ml in Equilibration buffer.

Equilibration Buffer

PBS Phosphate buffer 10 mM+0.14 M NaCl+0.0027 M KCl, pH 7.4 (Medicago)

Adsorption Buffer

PBS Phosphate buffer 10 mM+0.14 M NaCl+0.0027 M KCl, pH 7.4 (Medicago)

Elution Buffers

100 mM acetate pH 2.9

Dynamic Binding Capacity

2 ml of resin was packed in TRICORN™ 5 100 columns. The breakthrough capacity was determined with an ÄKTAExplorer 10 system at a residence time of 6 minutes (0.33 ml/min flow rate). Equilibration buffer was run through the bypass column until a stable baseline was obtained. This was done prior to auto zeroing. Sample was applied to the column until a 100% UV signal was obtained. Then, equilibration buffer was applied again until a stable baseline was obtained.

Sample was loaded onto the column until a UV signal of 85% of maximum absorbance was reached. The column was then washed with 5 column volumes (CV) equilibration buffer at flow rate 0.5 ml/min. The protein was eluted with 5 CV elution buffer at a flow rate of 0.5 ml/min. Then the column was cleaned with 0.5M NaOH at flow rate 0.2 ml/min and re-equilibrated with equilibration buffer.

For calculation of breakthrough capacity at 10%, the equation below was used. That is the amount of IgG that is loaded onto the column until the concentration of IgG in the column effluent is 10% of the IgG concentration in the feed.

$q_{10\%} = {\frac{C_{0}}{V_{c}}\left\lbrack {V_{app} - V_{sys} - {\int\limits_{V_{sys}}^{V_{app}}{\frac{{A(V)} - A_{sub}}{A_{100\%} - A_{sub}}*{dv}}}} \right\rbrack}$

-   -   A_(100%)=100% UV signal;     -   A_(sub)=absorbance contribution from non-binding IgG subclass;     -   A(V)=absorbance at a given applied volume;     -   V_(c)=column volume;     -   V_(app)=volume applied until 10% breakthrough;     -   V_(sys)=system dead volume;     -   C₀=feed concentration.

The dynamic binding capacity (DBC) at 10% breakthrough was calculated. The dynamic binding capacity (DBC) was calculated for 10 and 80% breakthrough.

CIP—0.5 M NaOH

The 10% breakthrough DBC (Qb10) was determined both before and after repeated exposures to alkaline cleaning solutions. Each cycle included a CIP step with 0.5 M NaOH pumped through the column at a rate of 0.5/min for 20 min, after which the column was left standing for 4 h. The exposure took place at room temperature (22+/−2° C.). After this incubation, the column was washed with equilibration buffer for 20 min at a flow rate of 0.5 ml/min. Table 4 shows the remaining capacity after six 4 h cycles (i.e. 24 h cumulative exposure time to 0.5 M NaOH), both in absolute numbers and relative to the initial capacity.

Example 5

Example 4 was repeated with the tetrameric ligands shown in Table 5, but with 1.0 M NaOH used in the CIP steps instead of 0.5 M. The results are shown in Table 5 and in FIG. 4 .

TABLE 5 Matrices with tetrametric ligands, evaluated in columns-1.0M NaOH. Remaining Capacity IgG Remaining retention Initial capacity IgG relative IgG Qb10 capacity to ref. SEQ Ligand capacity after six 4 after six 4 after ID content Qb10 h cycles h cycles six 4 h Ligand NO. (mg/ml) (mg/ml) (mg/ml) (%) cycles Zvar4 21 12 60.1 33.5 56 1 Zvar(Q9A, N11E, Q40V, 20 12.8 60.3 56.0 93 1.67 A42K, N43A, L44I)4 Zvar(N11K, H18K, S33K, 30 9.7 62.1 48.1 77 1.44 D37E, A42R, N43A, L44I, K50R, L51Y)4

Example 6

Base Matrices

The base matrices used were a set of rigid cross-linked agarose bead samples of 59-93 micrometers (volume-weighted, d50V) median diameter (determined on a Malvern Mastersizer 2000 laser diffraction instrument), prepared according to the methods of U.S. Pat. No. 6,602,990 and with a pore size corresponding to an inverse gel filtration chromatography Kd value of 0.62-0.82 for dextran of Mw 110 kDa, according to the methods described above, using HR10/30 columns (GE Healthcare) packed with the prototypes in 0.2 M NaCl and with a range of dextran fractions as probe molecules (flow rate 0.2 ml/min). The dry weight of the bead samples ranged from 53 to 86 mg/ml, as determined by drying 1.0 ml drained filter cake samples at 105° C. over night and weighing.

TABLE 6 Base matrix samples Base matrix Kd d50v (μm) Dry weight (mg/ml) A18 0.704 59.0 56.0 A20 0.70 69.2 55.8 A27 0.633 87.2 74.2 A28 0.638 67.4 70.2 A29 0.655 92.6 57.5 A32 0.654 73.0 70.5 A33 0.760 73.1 55.5 A38 0.657 70.9 56.2 A39 0.654 66.0 79.1 A40 0.687 64.9 74.9 A41 0.708 81.7 67.0 A42 0.638 88.0 59.4 A43 0.689 87.5 77.0 A45 0.670 56.6 66.0 A52 0.620 53.10 63.70 A53 0.630 52.6 86.0 A54 0.670 61.3 75.3 A55 0.640 62.0 69.6 A56 0.740 61.0 56.0 A56-2 0.740 51.0 56.0 A62a 0.788 48.8 70.1 A62b 0.823 50.0 46.9 A63a 0.790 66.8 59.6 A63b 0.765 54.0 79.0 A65a 0.796 58.0 60.0 A65b 0.805 57.3 46.0 B5 0.793 69.0 84.4 C1 0.699 71.0 73.4 C2 0.642 66.5 81.1 C3 0.711 62.0 82.0 C4 0.760 62.0 82.0 H31 0.717 82.0 59.0 H35 0.710 81.1 61.0 H40 0.650 52.8 65.0 I1 0.640 50.0 67.0 41 0.702 81.6 60.6 517 0.685 87.9 64.4 106 0.692 86.7 64.6 531C 0.661 51.7 63.8 P10 0.741 59.3 70.0 S9 0.736 64.1 72.2 Coupling

100 ml base matrix was washed with 10 gel volumes distilled water on a glass filter. The gel was weighed (1 g=1 ml) and mixed with 30 ml distilled water and 8.08 g NaOH (0.202 mol) in a 250 ml flask with an agitator. The temperature was adjusted to 27+/−2° C. in a water bath. 16 ml epichlorohydrin (0.202 mol) was added under vigorous agitation (about 250 rpm) during 90+/−10 minutes. The reaction was allowed to continue for another 80+/−10 minutes and the gel was then washed with >10 gel volumes distilled water on a glass filter until neutral pH was reached. This activated gel was used directly for coupling as below.

To 16.4 mL of ligand solution (50 mg/mL) in a 50 ml Falcon tube, 139 mg NaHCO₃, 17.4 mg Na₂CO₃, 143.8 mg NaCl and 141 mg EDTA, was added. The Falcon tube was placed on a roller table for 5-10 min, and then 63 mg of DTE was added. Reduction proceeded for >45 min. The ligand solution was then desalted on a PD10 column packed with Sephadex G-25. The ligand content in the desalted solution was determined by measuring the 276 nm UV absorption.

The activated gel was washed with 3-5 GV 10.1 M phosphate/1 mM EDTA pH 8.61 and the ligand was then coupled according to the method described in U.S. Pat. No. 6,399,750 5.2.2, although with considerably higher ligand amounts (see below). All buffers used in the experiments had been degassed by nitrogen gas for at least 5-10 min. The ligand content of the gels was controlled by varying the amount and concentration of the ligand solution, adding 5-20 mg ligand per ml gel. The ligand was either a tetramer (SEQ ID NO:20) or a hexamer (SEQ ID NO:33) of an alkali-stabilized mutant.

After immobilization the gels were washed 3×GV with distilled water. The gels+1 GV {0.1 M phosphate/1 mM EDTA/10% thioglycerol pH 8.6} was mixed and the tubes were left in a shaking table at room temperature overnight. The gels were then washed alternately with 3×GV {0.1 M TRIS/0.15 M NaCl pH 8.6} and 0.5 M HAc and then 8-10×GV with distilled water. Gel samples were sent to an external laboratory for amino acid analysis and the ligand content (mg/ml gel) was calculated from the total amino acid content.

Evaluation

The Qb10% dynamic capacity for polyclonal human IgG at 2.4 and 6 min residence time was determined as outlined in Example 4.

TABLE 7 Prototype results Ligand Base content Qb10% 2.4 Qb10% 6 Prototype matrix (mg/ml) Multimer min (mg/ml) min (mg/ml) N1 A38 7.45 tetramer 44.4 58.25 N2 A20 7.3 tetramer 45.12 57.21 N3 A42 6.72 tetramer 33.56 50.02 N4 A29 7.3 tetramer 36.34 51.8 N5 A28 7.9 tetramer 42.38 58.25 N6 A39 6.96 tetramer 41.88 54.67 N7 A27 7.5 tetramer 29.19 48.73 N8 A43 6.99 tetramer 33.43 49.79 N9 A38 11.34 tetramer 48.1 72.78 N10 A20 10.6 tetramer 50.66 70.07 N11 A42 11.1 tetramer 32.25 57.78 N12 A29 11 tetramer 34.85 64.68 N13 A28 11.9 tetramer 39.92 63.75 N14 A39 10.48 tetramer 44.37 64.79 N15 A27 12.1 tetramer 24.8 55.56 N16 A43 10.51 tetramer 31.82 58.04 N17 A41 8.83 tetramer 38.5 56.8 N18 A41 8.83 tetramer 37.84 58.6 N19 A41 8.83 tetramer 35.06 57.23 N20 A41 5.0 tetramer 35.64 46.04 N21 A41 13.0 tetramer 34.95 62.23 N22 A40 13.15 tetramer 56.85 71.09 N23 A33 7.33 tetramer 48.69 55.76 N24 A40 11.03 tetramer 54.96 73.8 033A A38 7.5 tetramer 44 58 033B A38 11.3 tetramer 48 73 097A A20 7.3 tetramer 45 57 097B A20 10.6 tetramer 51 70 003A A28 7.9 tetramer 42 58 003B A28 11.9 tetramer 40 64 003C A28 15.8 tetramer 37 67 038A A39 7.0 tetramer 42 55 038B A39 10.5 tetramer 44 65 074 A40 13.2 tetramer 57 71 093 A33 7.3 tetramer 49 56 058A A40 11.0 tetramer 55 74 077 A18 8.2 tetramer 52 59 010 A32 10.7 tetramer 40 57 099 A32 13.3 tetramer 37 66 030A B5 6.3 tetramer 32 38 030B B5 9.6 tetramer 45 47 293A C1 5.4 tetramer 38 47 293B C1 10.8 tetramer 43 60 294A C2 5.1 tetramer 39 46 294B C2 10.5 tetramer 42 57 336A H40 5.6 tetramer 47 52 336B H40 9.1 tetramer 52 67 091 A18 13.4 tetramer N/A 63 092 A20 12.8 tetramer 49 67 080 A33 9.4 tetramer 51 58 089 A40 6.1 tetramer 49 59 688A A62a 6.6 tetramer 41 46 688B A62a 14.8 tetramer 55 62 871 A62a 9.7 tetramer 48 60 934A A63a 6.6 tetramer 40 44 934B A63a 14.0 tetramer 48 56 017B A65a 13.1 tetramer 56 64 041A A62b 5.2 tetramer 40 N/A 041B A62b 11.1 tetramer 52 N/A 116A A65b 5.8 tetramer 42 46 116B A65b 8.8 tetramer 49 56 017A A65a 6.1 tetramer 40 44 387A A62a 6.4 tetramer 43 45 387B A62a 7.5 tetramer 47 56 432 A63a 6.1 tetramer 39 44 433A A65a 6.6 tetramer 42 47 433B A65a 13.6 tetramer 52 61 579A I1 6.1 tetramer 45 51 579B I1 11.2 tetramer 57 68 064A C3 5.9 tetramer 44 52 064B C3 9.0 tetramer 49 62 064C C3 14.3 tetramer 51 70 352A C4 10.1 tetramer 55 63 352B C4 14.4 tetramer 59 67 066A C3 6.8 hexamer 48 59 066B C3 11.9 hexamer 51 73 066C C3 15.1 hexamer 43 61 353A C4 11.2 hexamer 62 74 353B C4 15.2 hexamer 57 82 872A A62a 9.6 hexamer 56 72 872B A62a 14.5 hexamer 62 84 869A H40 6.9 hexamer 50 56 869B H40 14.3 hexamer 56 75 869C H40 23.0 hexamer 41 65 962A H35 6.8 hexamer 36 49 962B H35 12.3 hexamer 31 54 962C H35 20.3 hexamer 20 43 112A A56 7.9 hexamer 47 55 112B A56 12.4 hexamer 57 73 112C A56 19.2 hexamer 55 80 113A A56 7.1 hexamer 48 57 113B A56 12.4 hexamer 53 73 113C A56 15.2 hexamer 48 76 212A H31 6.5 hexamer 37 38 212B H31 10.4 hexamer 50 61 212C H31 20.0 hexamer 31 52 213A A33 6.5 hexamer 44 53 213B A33 10.9 hexamer 50 65 213C A33 11.1 hexamer 50 68 432A A20 6.4 hexamer 41 56 432B A20 12.4 hexamer 38 64 432C A20 21.1 hexamer 44 43 433A A38 5.9 hexamer 47 57 433B A38 11.6 hexamer 48 72 433C A38 15.8 hexamer 36 62 742A A54 6.7 hexamer 38 46 742B A54 12.6 hexamer 45 52 742C A54 21.1 hexamer 38 65 726A A63b 6.4 hexamer 42 46 726B A63b 10.6 hexamer 49 60 726C A63b 16.7 hexamer 53 69 793A A56-2 6.8 hexamer 50 58 793B A56-2 12.5 hexamer 59 72 793C A56-2 19.2 hexamer 61 82 517 517 12.0  tetramer* 35 56 106 106 5.8  tetramer* 33 45 531C 531C 11.2  tetramer* 54 65 P10 P10 19.0 hexamer 76 S9 S9 18.4 hexamer 56 75 *SEQ ID NO: 21

Example 7

A series of prototypes, prepared as above, with different ligand content (tetramer, SEQ ID NO:20) were incubated in 1 M NaOH for 4, 8 and 31 hours at 22+/−2° C. and the dynamic IgG capacity (Qb10%, 6 min residence time) was measured before and after incubation. The prototypes are shown in Table 8 and the results in FIGS. 5 and 6 . It can be seen that the stability towards this harsh alkali treatment increases with increasing ligand content.

TABLE 8 Samples for incubation in 1M NaOH Ligand content Qb10%, 6 min, before Prototype (mg/ml) incubation (mg/ml) N1 12 78 LE28 13 79 N17 16 73 N16 20 73

Example 8

Pressure-Flow Testing of Matrices

300 ml sedimented matrix was packed in a FINELINE 35 column (GE Healthcare Life Sciences, Uppsala, Sweden), with 35 mm inner diameter and 330 mm tube height. The gel was suspended in distilled water to produce a slurry volume of 620 ml and the height of the packed bed was 300+/−10 mm. The packing pressure was 0.10+/−0.02 bar (10+/−2 kPa). Distilled water was then pumped through the column at increasing pump rates and the flow rate (expressed as the linear flow velocity, cm/h) and back pressure (MPa) was measured after 5 min for each pump setting. The measurements were continued until a max flow rate and a max pressure was reached, i.e. the flow rate and back pressure achieved when the flow rate starts to diminish at increasing back pressures.

TABLE 9 Pressure flow performance of matrices Matrix Max flow velocity, cm/h Max pressure (MPa) 517 1343 0.56 106 1306 0.56 531C 513 0.51 P10 862 0.60 S9 1172 0.64 The P10 and S9 matrices have a higher rigidity, as indicated by the max pressure, and can thus sustain comparatively high flow velocities despite their low (59-64 micrometers) median particle diameters.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. All patents and patent applications mentioned in the text are hereby incorporated by reference in their entireties, as if they were individually incorporated.

ITEMIZED LIST OF EMBODIMENTS

i. An Fc-binding polypeptide which comprises a sequence as defined by, or having at least 90% or at least 95% or 98% identity to SEQ ID NO:53.

 (SEQ ID NO: 53) X₁Q X₂AFYEILX₃LP NLTEEQRX₄X₅F IX₆X₇LKDX₈PSX₉ SX₁₀X₁₁X₁₂LAEAKX₁₃ X₁₄NX₁₅AQ wherein individually of each other: X₁=A or Q or is deleted X₂=E, K, Y, T, F, L, W, I, M, V, A, H or R X₃=H or K X₄=A or N X₅=A, G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K X₆=Q or E X₇=S or K X₈=E or D X₉=Q or V or is deleted X₁₀=K, R or A or is deleted X₁₁=A, E or N or is deleted X₁₂=J or L X₁₃=K or R X₁₄=L or Y X₁₅=D, F, Y, W, K or R ii. The polypeptide of embodiment i, wherein: X₁=A or is deleted, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V or is deleted, X₁₀=K or is deleted, X₁₁=A or is deleted, X₁₂=I, X₁₃=K, X₁₄=L. iii. The polypeptide of embodiment i or ii, wherein X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D. iv. The polypeptide of embodiment i or ii, wherein X₁ is deleted, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D. v. The polypeptide of embodiment i or ii, wherein X₁=A, X₂=E, X₃=H, X₄=N, X₅=S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D. vi. The polypeptide of embodiment i or ii, wherein X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉ is deleted, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D. vii. The polypeptide of embodiment i or ii, wherein X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀ is deleted, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D. viii. The polypeptide of embodiment i or ii, wherein X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁ is deleted, X₁₂=I, X₁₃=K, X₁₄=Land X₁₅=D. ix. The polypeptide of embodiment i or ii, wherein X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=F, Y, W, K or R. x. An Fc-binding polypeptide comprising a mutant of a parental Fc-binding domain of Staphylococcus Protein A (SpA), as defined by, or having at least 90% such as at least 95% or 98% identity to, SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO:3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:22, SEQ ID NO:51 or SEQ ID NO:52, wherein at least the asparagine or serine residue at the position corresponding to position 11 in SEQ ID NO:4-7 has been mutated to an amino acid selected from the group consisting of glutamic acid, lysine, tyrosine, threonine, phenylalanine, leucine, isoleucine, tryptophan, methionine, valine, alanine, histidine and arginine. xi. The polypeptide of embodiment x, comprising a mutant of a parental Fc-binding domain of Staphylococcus Protein A (SpA), as defined by, or having at least 90% such as at least 95% or 98% identity to, SEQ ID NO:51 or SEQ ID NO:52. xii. The polypeptide of embodiment x or xi, wherein the amino acid residue at the position corresponding to position 11 in SEQ ID NO:4-7 is a glutamic acid. xiii. The polypeptide of any one of embodiments x-xii, wherein the amino acid residue at the position corresponding to position 11 in SEQ ID NO:4-7 is a lysine. xiv. The polypeptide of any one of embodiments x-xiii, wherein the amino acid residue at the position corresponding to position 29 in SEQ ID NO:4-7 is a glycine, serine, tyrosine, glutamine, threonine, asparagine, phenylalanine, leucine, tryptophan, isoleucine, methionine, valine, aspartic acid, glutamic acid, histidine, arginine or lysine. xv. The polypeptide of any one of embodiments x-xiv, wherein the amino acid residue at the position corresponding to position 9 in SEQ ID NO:4-7 is an alanine. xvi. The polypeptide of any one of embodiments x-xv, wherein the amino acid residue at the position corresponding to position 9 in SEQ ID NO:4-7 has been deleted. xvii. The polypeptide of any one of embodiments x-xvi, wherein the amino acid residue at the position corresponding to position 50 in SEQ ID NO:4-7 is an arginine or a glutamic acid, such as an arginine. xviii. The polypeptide of any one of embodiments x-xvii, wherein the amino acid residue at the position corresponding to position 43 in SEQ ID NO:4-7 has been deleted. xix. The polypeptide of any one of embodiments x-xviii, wherein the amino acid residue at the position corresponding to position 28 in SEQ ID NO:4-7 is an alanine or an asparagine. xx. The polypeptide of any one of embodiments x-xix, wherein the amino acid residue at the position corresponding to position 40 in SEQ ID NO:4-7 is selected from the group consisting of asparagine, alanine, glutamic acid and valine. xxi. The polypeptide of any one of embodiments x-xx, wherein the amino acid residue at the position corresponding to position 40 in SEQ ID NO:4-7 has been deleted. xxii. The polypeptide according to any one of embodiments x-xxi, wherein the amino acid residue at the position corresponding to position 42 in SEQ ID NO:4-7 is an alanine, lysine or arginine, such as an arginine. xxiii. The polypeptide according to any one of embodiments x-xxii, wherein the amino acid residue at the position corresponding to position 42 in SEQ ID NO:4-7 has been deleted. xxiv. The polypeptide according to any one of embodiments x-xxiii, wherein the amino acid residue at the position corresponding to position 44 in SEQ ID NO:4-7 is a leucine or an isoleucine, such as an isoleucine. xxv. The polypeptide according to any one of embodiments x-xxiv, wherein the amino acid residue at the position corresponding to position 44 in SEQ ID NO:4-7 has been deleted. xxvi. The polypeptide according to any one of embodiments x-xxv, wherein the amino acid residue at the position corresponding to position 53 in SEQ ID NO:4-7 is a phenylalanine, a tyrosine, a tryptophan, an arginine or a lysine. xxvii. The polypeptide according to any one of embodiments x-xxvi, wherein the amino acid residue at the position corresponding to position 18 in SEQ ID NO:4-7 is a lysine or a histidine, such as a lysine. xxviii. The polypeptide according to any one of embodiments x-xxvii, wherein the amino acid residue at the position corresponding to position 33 in SEQ ID NO:4-7 is a lysine or a serine, such as a lysine. xxix. The polypeptide according to any one of embodiments x-xxviii, wherein the amino acid residue at the position corresponding to position 37 in SEQ ID NO:4-7 is a glutamic acid or an aspartic acid, such as a glutamic acid. xxx. The polypeptide according to any one of embodiments x-xxix, wherein the amino acid residue at the position corresponding to position 51 in SEQ ID NO:4-7 is a tyrosine or a leucine, such as a tyrosine. xxxi. The polypeptide according to any one of embodiments x-xxx, wherein one or more of the amino acid residues at the positions corresponding to positions 1, 2, 3, 4, 5, 6, 7, 8, 56, 57 or 58 in SEQ ID NO: 4-7 have been deleted. xxxii. The polypeptide according to any one of embodiments x-xxxi, wherein the mutation is selected from the group consisting of: Q9A, N11E, A29G, Q40V, A42K, N43A, L44I; Q9A, N11E, A29S, Q40V, A42K, N43A, L44I; Q9A, N11E, A29Y, Q40V, A42K, N43A, L44I; Q9A, N11E, A29Q, Q40V, A42K, N43A, L44I; Q9A, N11E, A29T, Q40V, A42K, N43A, L44I; Q9A, N11E, A29N, Q40V, A42K, N43A, L44I; Q9A, N11E, A29F, Q40V, A42K, N43A, L44I; Q9A, N11E, A29L, Q40V, A42K, N43A, L44I; Q9A, N11E, A29W, Q40V, A42K, N43A, L44I; Q9A, N11E, A29I, Q40V, A42K, N43A, L44I; Q9A, N11E, A29M, Q40V, A42K, N43A, L44I; Q9A, N11E, A29V, Q40V, A42K, N43A, L44I; Q9A, N11E, A29D, Q40V, A42K, N43A, L44I; Q9A, N11E, A29E, Q40V, A42K, N43A, L44I; Q9A, N11E, A29H, Q40V, A42K, N43A, L44I; Q9A, N11E, A29R, Q40V, A42K, N43A, L44I; and Q9A, N11E, A29K, Q40V, A42K, N43A, L44I. xxxiii. The polypeptide according to any one of embodiments x-xxxii, wherein the mutation is selected from the group consisting of: Q9A, N11E, Q40V, A42K, N43A, L44I, D53F; Q9A, N11E, Q40V, A42K, N43A, L44I, D53Y; Q9A, N11E, Q40V, A42K, N43A, L44I, D53W; Q9A, N11E, Q40V, A42K, N43A, L44I, D53K; and Q9A, N11E, Q40V, A42K, N43A, L44I, D53R. xxxiv. The polypeptide according to any one of embodiments x-xxxiii, wherein the mutation is selected from the group consisting of: Q9del, N11E, Q40V, A42K, N43A, L44I; Q9A, N11E, Q40del, A42K, N43A, L44I; Q9A, N11E, Q40V, A42del, N43A, L44I; and Q9A, N11E, Q40V, A42K, N43del, L44I. xxxv. The polypeptide according to any one of embodiments x-xxxiv, wherein the mutation is selected from the group consisting of: D2del, A3del, K4del, Q9A, N11E, Q40V, A42K, N43A, L44I; V1del, D2del, Q9A, N11E, Q40V, A42K, N43A, L44I, K58del; V1del, D2del, A3del, Q9A, N11E, Q40V, A42K, N43A, L44I, P57del, K58del; K4del, F5del, D6del, K7del, E8del, Q9A, N11E, Q40V, A42K, N43A, L44I; Q9A, N11E, Q40V, A42K, N43A, L44I, A56del, P57del, K58del; V1del, D2del, A3del, Q9A, N11E, Q40V, A42K, N43A, L44I; V1del, D2del, A3del, K4del, F5del, D6del, K7del, E8del, Q9A, N11E, Q40V, A42K, N43A, L44I; and Q9A, N11E, Q40V, A42K, N43A, L44I, K58_insYEDG. xxxvi. The polypeptide according to any one of embodiments i-xxxi, comprising or consisting essentially of a sequence having at least 90% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60, SEQ ID NO:61, SEQ ID NO:62, SEQ ID NO:63, SEQ ID NO:64, SEQ ID NO:65, SEQ ID NO:66, SEQ ID NO:67, SEQ ID NO:68, SEQ ID NO:69 and SEQ ID NO:70. xxxvii. The polypeptide according to any one of embodiments i-xxxi, comprising or consisting essentially of a sequence having at least 90% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:71, SEQ ID NO:72, SEQ ID NO:73, SEQ ID NO:74 and SEQ ID NO:75. xxxviii. The polypeptide according to any one of embodiments i-xxxi, comprising or consisting essentially of a sequence having at least 90% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:76, SEQ ID NO:77, SEQ ID NO:78 and SEQ ID NO:79. xxxix. The polypeptide according to any one of embodiments i-xxxi, comprising or consisting essentially of a sequence having at least 90% identity to an amino acid sequence selected from the group consisting of: SEQ ID NO:89, SEQ ID NO:90, SEQ ID NO:91, SEQ ID NO:92, SEQ ID NO:93, SEQ ID NO:94 and SEQ ID NO:95. xl. The polypeptide according to any preceding embodiment, which polypeptide has an improved alkaline stability compared to a polypeptide as defined by SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6 or SEQ ID NO:7, such as by SEQ ID NO:7. xli. The polypeptide according to any preceding embodiment, which polypeptide has an improved alkaline stability compared to a parental polypeptide as defined by SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6 or SEQ ID NO:7, such as by SEQ ID NO:7. xlii. The polypeptide according to embodiment xl or xli, wherein the alkaline stability is improved as measured by the remaining IgG-binding capacity, after 24, 25 h incubation in 0.5 M or 1.0 M aqueous NaOH at 22+/−2° C. xliii. A multimer comprising or consisting essentially of a plurality of polypeptides as defined by any preceding embodiment. xliv. The multimer according to embodiment xliii, wherein the polypeptides are linked by linkers comprising up to 25 amino acids, such as 3-25 or 3-20 amino acids. xlv. The multimer of embodiment xliii or xliv, wherein at least two polypeptides are linked by linkers comprising or consisting essentially of a sequence having at least 90% identity with an amino acid sequence selected from the group consisting of APKVDAKFDKE (SEQ ID NO:96), APKVDNKFNKE (SEQ ID NO:97), APKADNKFNKE (SEQ ID NO:98), APKVFDKE (SEQ ID NO:99), APAKFDKE (SEQ ID NO:100), AKFDKE (SEQ ID NO:101), APKVDA (SEQ ID NO:102), VDAKFDKE (SEQ ID NO:103), APKKFDKE (SEQ ID NO:104), APK, APKYEDGVDAKFDKE (SEQ ID NO:105) and YEDG (SEQ ID NO:106). xlvi. The multimer according to embodiment xliv or xlv, which is a dimer, trimer, tetramer, pentamer, hexamer, heptamer, octamer or nonamer. xlvii. The multimer according to any one of embodiments xliv-xlvi, which comprises or consists essentially of a sequence selected from the group of sequences defined by SEQ ID NO:80, SEQ ID NO:81, SEQ ID NO:82, SEQ ID NO:83, SEQ ID NO:84, SEQ ID NO:85, SEQ ID NO:86 and SEQ ID NO:87. xlviii. The polypeptide or multimer according to any preceding embodiment, further comprising at, or within 1-5 amino acid residues from, the C-terminal or N-terminal one or more coupling element, selected from the group consisting of one or more cysteine residues, a plurality of lysine residues and a plurality of histidine residues. xlix. A nucleic acid or a vector encoding a polypeptide or multimer according to any preceding embodiment. l. An expression system, which comprises a nucleic acid or vector according to embodiment xlix. li. A separation matrix, wherein a plurality of polypeptides or multimers according to any one of embodiment i-xlviii have been coupled to a solid support. lii. A separation matrix comprising at least 11 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein: a) said ligands comprise multimers of alkali-stabilized Protein A domains, b) said porous support comprises cross-linked polymer particles having a volume-weighted median diameter (d50, v) of 55-70 micrometers and a dry solids weight of 55-80 mg/ml. liii. A separation matrix comprising at least 15, such as 15-21 or 15-18 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein said ligands comprise multimers of alkali-stabilized Protein A domains. liv. The separation matrix of embodiment li or liii, wherein said cross-linked polymer particles comprise cross-linked polysaccharide particles. lv. The separation matrix of any one of embodiments li-liv, wherein said cross-linked polymer particles comprise cross-linked agarose particles. lvi. The separation matrix of any one of embodiments li-lv, wherein said cross-linked polymer particles have a pore size corresponding to an inverse gel filtration chromatography Kd value of 0.70-0.85 for dextran of Mw 110 kDa. lvii. The separation matrix of any one of embodiments li-lvi, which has a max pressure of at least 0.58, such as at least 0.60, MPa when packed at 300+/−10 mm bed height in a FINELINE 35 column. lviii. The separation matrix of any one of embodiments li-lvii, wherein said multimers comprise tetramers, pentamers, hexamers or heptamers of alkali-stabilized Protein A domains. lix. The separation matrix of any one of embodiments li-lviii, wherein said multimers comprise hexamers of alkali-stabilized Protein A domains. lx. The separation matrix of any one of embodiments li-lix, wherein the polypeptides are linked by linkers comprising up to 25 amino acids, such as 3-25 or 3-20 amino acids. lxi. The separation matrix of any one of embodiments li-lx, wherein at least two polypeptides are linked by linkers comprising or consisting essentially of a sequence having at least 90% identity with an amino acid sequence selected from the group consisting of APKVDAKFDKE (SEQ ID NO:96), APKVDNKFNKE (SEQ ID NO:97), APKADNKFNKE (SEQ ID NO:98), APKVFDKE (SEQ ID NO:99), APAKFDKE (SEQ ID NO:100), AKFDKE (SEQ ID NO:101), APKVDA (SEQ ID NO:102), VDAKFDKE (SEQ ID NO:103), APKKFDKE (SEQ ID NO:104), APK, APKYEDGVDAKFDKE (SEQ ID NO:105) and YEDG (SEQ ID NO:106). lxii. The separation matrix of any one of embodiments li-lxi, having a 10% breakthrough dynamic binding capacity for IgG of at least 45 mg/ml, such as at least 50 or at least 55 mg/ml mg/ml at 2.4 min residence time. lxiii. The separation matrix of any one of embodiments li-lxii, having a 10% breakthrough dynamic binding capacity for IgG of at least 60 mg/ml, such as at least 65, at least 70 or at least 75 mg/ml at 6 min residence time. lxiv. The separation matrix of any one of embodiments li-lxiii, wherein the 10% breakthrough dynamic binding capacity for IgG at 2.4 or 6 min residence time is reduced by less than 20% after incubation 31 h in 1.0 M aqueous NaOH at 22+/−2 C. lxv. The separation matrix of any one of embodiments li-lxiv, having a dissociation constant for IgG2 of below 0.2 mg/ml, such as below 0.1 mg/ml, in 20 mM phosphate buffer, 180 mM NaCl, pH 7.5. lxvi. The separation matrix according to any one of embodiments li-lxv, wherein the polypeptides or multimers have been coupled to the solid support or porous support via thioether bonds. lxvii. The separation matrix according to any one of embodiments li-lxvi, wherein the solid support or porous support is a polysaccharide. lxviii. The separation matrix according to any one of embodiments li-lxvii, wherein the IgG capacity of the matrix after 24 incubation in 0.5 M NaOH at 22+/−2° C. is at least 80, such as at least 85, at least 90 or at least 95% of the IgG capacity before the incubation. lxix. The separation matrix according to any one of embodiments li-lxviii, wherein the IgG capacity of the matrix after 24 incubation in 1.0 M NaOH at 22+/−2° C. is at least 70, such as at least 80 or at least 90% of the IgG capacity before the incubation. lxx. The separation matrix of any one of embodiments li-lxix, wherein said alkali-stabilized Protein A domains or plurality of polypeptides/multimers comprise(s) mutants of a parental Fc-binding domain of Staphylococcus Protein A (SpA), as defined by, or having at least 80% such as at least 90%, 95% or 98% identity to, SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO:3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:22, SEQ ID NO:51 or SEQ ID NO:52, wherein at least the asparagine or serine residue at the position corresponding to position 11 in SEQ ID NO:4-7 has been mutated to an amino acid selected from the group consisting of glutamic acid, lysine, tyrosine, threonine, phenylalanine, leucine, isoleucine, tryptophan, methionine, valine, alanine, histidine and arginine. lxxi. The separation matrix of embodiment lxx, wherein the amino acid residue at the position corresponding to position 11 in SEQ ID NO:4-7 is, or has been mutated to, a glutamic acid or a lysine. lxxii. The separation matrix of embodiment lxx or lxxi, wherein the amino acid residue at the position corresponding to position 40 in SEQ ID NO:4-7 is, or has been mutated to, a valine. lxxiii. The separation matrix of any one of embodiments li-lxix, wherein said alkali-stabilized Protein A domains or plurality of polypeptides/multimers comprise(s) an Fc-binding polypeptide having an amino acid sequence as defined by, or having at least 80%, such as at least 90, 95 or 98%, identity to SEQ ID NO:53.

 (SEQ ID NO: 53) X₁Q X₂AFYEILX₃LP NLTEEQRX₄X₅F IX₆X₇LKDX₈PSX₉ SX₁₀X₁₁X₁₂LAEAKX₁₃ X₁₄NX₁₅AQ wherein individually of each other: X₁=A or Q or is deleted X₂=E, K, Y, T, F, L, W, I, M, V, A, H or R X₃=H or K X₄=A or N X₅=A, G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K X₆=Q or E X₇=S or K X₈=E or D X₉=Q or V or is deleted X₁₀=K, R or A or is deleted X₁₁=A, E or N or is deleted X₁₂=J or L X₁₃=K or R X₁₄=L or Y X₁₅=D, F, Y, W, K or R lxxiv. The separation matrix of embodiment lxxiiii, wherein individually of each other: X₁=A or is deleted, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V or is deleted, X₁₀=K or is deleted, X₁₁=A or is deleted, X₁₂=I, X₁₃=K, X₁₄=L. lxxv. The separation matrix of embodiment lxxiii, wherein individually of each other: X₁=A, X₂=E, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=L and X₁₅=D. lxxvi. The separation matrix of embodiment lxxiii, wherein individually of each other: wherein X₁ is A, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=Land X₁₅=D. lxxvii. The separation matrix of embodiment lxxiii, wherein individually of each other: wherein X₁ is A, X₃=H, X₄=N, X₅=A, X₆=Q, X₇=S, X₈=D, X₉=V, X₁₀=K, X₁₁=A, X₁₂=I, X₁₃=K, X₁₄=Land X₁₅=D. lxxviii. The separation matrix according to any one of embodiments li-lxxvii, wherein said multimers or polypeptides further comprise at, or within 1-5 amino acid residues from, the C-terminal or N-terminal one or more coupling element, selected from the group consisting of one or more cysteine residues, a plurality of lysine residues and a plurality of histidine residues. lxxix. The separation matrix according to any one of embodiments li-lxxviii wherein said multimers or polypeptides further comprise at the N-terminal a leader sequence, comprising 1-20 amino acid residues. lxxx. A method of isolating an immunoglobulin, wherein a separation matrix according to any one of embodiments li-lxxix is used. lxxxi. The method of embodiment lxxx, comprising the steps of: a) contacting a liquid sample comprising an immunoglobulin with a separation matrix according to any one of embodiments li-lxxix, b) washing said separation matrix with a washing liquid, c) eluting the immunoglobulin from the separation matrix with an elution liquid, and d) cleaning the separation matrix with a cleaning liquid. lxxxii. The method of embodiment lxxxi, wherein the cleaning liquid is alkaline, such as with a pH of 13-14. lxxxiii. The method of embodiment lxxxi or lxxxii, wherein the cleaning liquid comprises 0.1-1.0 M NaOH or KOH, such as 0.5-1.0 M or 0.4-1.0 M NaOH or KOH. lxxxiv. The method of any one of embodiments lxxxi-lxxxiii, wherein steps a)-d) are repeated at least 10 times, such as at least 50 times or 50-200 times. lxxxv. The method of any one of embodiments lxxxi-lxxxiv, wherein steps a)-c) are repeated at least 10 times, such as at least 50 times or 50-200 times and wherein step d) is performed after a plurality of instances of step c), such as at least 10 or at least 50 times. 

The invention claimed is:
 1. A separation matrix comprising at least 15 mg/ml Fc-binding ligands covalently coupled to a porous support, wherein: a) said ligands comprise multimers of alkali-stabilized Protein A domains, b) said porous support comprises cross-linked polymer particles having a volume-weighted median diameter (d50, v) of from 56 micrometers to 70 micrometers and a dry solids weight of from 55 mg/ml to 80 mg/ml.
 2. The separation matrix of claim 1, wherein said cross-linked polymer particles have a volume-weighted median diameter (d50, v) of from 56 micrometers to 66 micrometers.
 3. The separation matrix of claim 1, wherein said cross-linked polymer particles have a dry solids weight of from 60 mg/ml to 78 mg/ml.
 4. The separation matrix of claim 3, wherein said cross-linked polymer particles have a dry solids weight of from 65 mg/ml to 78 mg/ml.
 5. The separation matrix of claim 1, wherein said separation matrix has a max pressure of at least 0.58 MPa when packed at 300+/−10 mm bed height in a 35 mm separation column.
 6. The separation matrix of claim 1, wherein said cross-linked polymer particles comprise cross-linked polysaccharide particles.
 7. The separation matrix of claim 1, wherein said cross-linked polymer particles comprise cross-linked agarose particles.
 8. The separation matrix of claim 1, wherein said cross-linked polymer particles have a pore size corresponding to an inverse gel filtration chromatography Kd value of 0.69-0.85 for dextran of Mw 110 kDa.
 9. The separation matrix of claim 1, wherein said multimers comprise tetramers, pentamers, hexamers or heptamers of alkali-stabilized Protein A domains.
 10. The separation matrix of claim 1, wherein said multimers comprise hexamers of alkali-stabilized Protein A domains.
 11. The separation matrix of claim 1, having a 10% breakthrough dynamic binding capacity for IgG of at least 45 mg/ml at 2.4 min residence time.
 12. The separation matrix of claim 1, having a 10% breakthrough dynamic binding capacity for IgG of at least 60 mg/ml at 6 min residence time.
 13. The separation matrix of claim 11, wherein the 10% breakthrough dynamic binding capacity for IgG at 2.4 min residence time is reduced by less than 20% after incubation 31 h in 1.0 M aqueous NaOH at 22+/−2 C.
 14. The separation matrix of claim 1, having a dissociation constant for IgG2 of below 0.2 mg/ml in 20 mM phosphate buffer, 180 mM NaCl, pH 7.5.
 15. The separation matrix of claim 1, wherein said alkali-stabilized Protein A domains comprise an Fc-binding polypeptide having an amino acid sequence as defined by, or having at least 80% identity to SEQ ID NO:53 and X₁Q X₂AFYEILX₃LP NLTEEQRX₄X₅F IX₆X₇LKDX₈PSX₉ SX₁₀X₁₁X₁₂LAEAKX₁₃ X₁₄NX₁₅AQ (SEQ ID NO:53) wherein individually of each other: X₁=A or Q or is deleted X₂=E, K, Y, T, F, L, W, I, M, V, A, H or R X₃=H or K X₄=A or N X₅=A, G, S, Y, Q, T, N, F, L, W, I, M, V, D, E, H, R or K X₆=Q or E X₇=S or K X₈=E or D X₉=Q or V or is deleted X₁₀=K, R or A or is deleted X₁₁=A, E or N or is deleted X₁₂=I or L X₁₃=K or R X₁₄=L or Y X₁₅=D, F, Y, W, K or R.
 16. The separation matrix of claim 15, wherein individually of each other: X₁=A or is deleted, X₂=E, X₃=H, X₄=N, X₆=Q, X₇=S, X₈=D, X₉=V or is deleted, X₁₀=K or is deleted, X₁₁=A or is deleted, X₁₂=I, X₁₃=K, X₁₄=L.
 17. The separation matrix of claim 15, wherein said multimers comprise hexamers of alkali-stabilized Protein A domains.
 18. The separation matrix of claim 15, wherein the amino acid sequence has at least 90% identity to SEQ ID NO:53.
 19. The separation matrix of claim 15, wherein the amino acid sequence has at least 95% identity to SEQ ID NO:53.
 20. The separation matrix of claim 15, wherein the amino acid sequence has at least 98% identity to SEQ ID NO:53.
 21. The separation matrix of claim 15, wherein the amino acid sequence is identical to SEQ ID NO:53.
 22. The separation matrix of claim 1, wherein the polypeptides are linked by linkers comprising up to 25 amino acids.
 23. The separation matrix of claim 1, wherein at least two polypeptides are linked by linkers comprising or consisting essentially of a sequence having at least 90% identity with an amino acid sequence selected from the group consisting of APKVDAKFDKE (SEQ ID NO:96, APKVDNKFNKE (SEQ ID NO:97), APKADNKFNKE (SEQ ID NO:98), APKVFDKE (SEQ ID NO:99), APAKFDKE (SEQ ID NO:100), AKFDKE (SEQ ID NO:101), APKVDA (SEQ ID NO:102), VDAKFDKE (SEQ ID NO:103), APKKFDKE (SEQ ID NO:104), APK, APKYEDGVDAKFDKE (SEQ ID NO:105) and YEDG (SEQ ID NO:106).
 24. The separation matrix of claim 1, comprising from 15 mg/ml to 21 mg/ml Fc-binding ligands covalently coupled to the porous support.
 25. The separation matrix of claim 1, comprising from 17 mg/ml to 21 mg/ml Fc-binding ligands covalently coupled to the porous support.
 26. The separation matrix of claim 1, comprising from 18 mg/ml to 20 mg/ml Fc-binding ligands covalently coupled to the porous support.
 27. The separation matrix of claim 1 having a 10% breakthrough dynamic binding capacity for IgG of at least 50 mg/ml at 2.4 min residence time.
 28. The separation matrix of claim 1 having a 10% breakthrough dynamic binding capacity for IgG of at least 55 mg/ml at 2.4 min residence time.
 29. The separation matrix of claim 1, having a 10% breakthrough dynamic binding capacity for IgG of at least 65 mg/ml at 6 min residence time.
 30. The separation matrix of claim 1, having a 10% breakthrough dynamic binding capacity for IgG of at least 70 mg/ml at 6 min residence time.
 31. The separation matrix of claim 1, having a 10% breakthrough dynamic binding capacity for IgG of at least 75 mg/ml at 6 min residence time.
 32. The separation matrix of claim 1 having a dissociation constant for IgG2 of below 0.1 mg/ml in 20 mM phosphate buffer, 180 mM NaCl, pH 7.5.
 33. A method of isolating an immunoglobulin, comprising the steps of: a) contacting a liquid sample comprising an immunoglobulin with a separation matrix according to claim 1, b) washing said separation matrix with a washing liquid, c) eluting the immunoglobulin from the separation matrix with an elution liquid, and d) cleaning the separation matrix with a cleaning liquid.
 34. The method of claim 33, wherein the cleaning liquid comprises from 0.1 to 1.0 M NaOH or KOH.
 35. The method of claim 33, wherein steps a)-d) are repeated at least 10 times.
 36. The method of claim 33, wherein in step c) said elution liquid has a pH of from 2.5 to 4.5.
 37. The method of claim 33, wherein in step a) the pH is from 6 to
 8. 38. The method of claim 33, wherein in step a) the residence time of said liquid sample on said separation matrix is from 2 minutes to 20 minutes.
 39. The method of claim 33, wherein the cleaning liquid comprises at least 0.5 M NaOH.
 40. The method of claim 33, wherein in step d) the contact time between the separation matrix and the cleaning liquid is less than 10 min. 